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QM34  B91  1912     The  anatomy  of  the  b 


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BURKHOIDER 


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Columbia  Wini^tv^it^  '  ^  ' 
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Anatomy  of  the  Brain 


A  Manual  for  Students  and 
Practitioners    of    Medicine 


THE  BRAIN  OF  THE  SHEEP  (OVIS  ARIES)  BEING  SELECTED 

FOR    DESCRIPTION    AND    ILLUSTRATION   BECAUSE 

OF   ITS  AVAILABILITY    AND    ITS   PRACTICAL 

IDENTITY    WITH    THE    HUMAN    BRAIN 

FOR  LABORATORY   USE. 


S})  J.  F.  BURKHOLDER,  M.  D. 

Professor    of    Ophthalmology  ir»    the  School   of 
Medicine   of   the   Loyola    University. 


Q    OGX)    B 

With  an   Introduction   by 

PROF.  HENRY  H.  DONALDSON 

B     OGX)     Q 


WITH    FORTY    Pl'M.   PAGE   PI,ATKS    (.SIX   OP   THEM   COLORED) 
FROM   ORIGINAI-   DRAWINGS     BT   THE    AUTHOR. 


C.  P.  ENGELHARD  &  COMPANY 
Chicago  1912 


>/vqJ^ 


Copyright,  1912. 
G.  P.  Engelhard  &  Company. 


CONTENTS. 

Pag.- 

I'lcl'acf    t;>    First    iMlition 7  !) 

Prefaoi-    to    Second   Edition ]  l-]2 

lutroduf'lioii     l;)-14 

CHAPTEPv   I. — The   Brain — Its   Penioval    and    I'rcj)  iration.  .  .  15-16 

CHAPTEP  IT.— Coverino-s    of    llie    Brain 17-18 

CHAPTEPv   III.— Dura    IMater    Eneepliali 19-23 

CHAPTER  IV. — Araclinoidea   Encepliali    24-25 

CHAPTER  v.— Pia    Mator    Encepliali 26-27 

CHAPTER  ^"I.— Blood  Vessels  at  the  Base  of  tlic   P.rain 28-30 

CHAPTER  VIE— External   Surface   of  the   Brain 31-32 

CHAPTER  VIII.— Dorsal   Snrface  of  the   (V  idiruin 33.37 

CHAPTER  IX.— Dorsal  Surface  of  the  Cerel.ruui 38-40 

CHAPTER  X. — Lateral    Surface   of   the    Cerehruni 41-42 

CHAPTER  XL— Ventral    Surface   of    the    Cen  lirum 43-46 

CHAPTER  XII.  —The   Medulla    Oblongata 47-48 

CLTAPTER  XIII. — Mesial     Surface    of    Cereliruni     and     Cere- 
bellum       49-54 

CHAPTER  XIV.-— Cerebral   Substance  and   Corpus   Callosuni.  .i.l  GO 

CHAPTER  XA'.- The    Lateral    Ventricles Ul-(i4 

CHAPTKR  XVI. —The    Fornix    65-66 

CHAPTER  X^'rI.— The    Hippocampus 67-61) 

CHAPTER  X\lir.— Tiie   Optic   Thalamus 70-74 

CHAPTER  XIX.— The   Pineal   Body *'....  75-76 

CHAPTER  XX. — The    .Viiterior    Conunissure 77-7!t 

CHAPTER  XXL— The    Tliird    Ventricle 80-8! 

CHAPTER  XXIL-The   (  orpora    Quadrigemina 82-8M 

CHAPTER   XXUr.— Cerebral    Peduncles 84-86 

(  IIAPTER    .\.\IV.— Tin-    P.ms    87-89 

(  IIAPTER  XXV.— The    Tra|)e/.inni 90-92 

CHARTER  XX VI.— Structure    of    llie    .Medulla     Oblongata— 

Ventral    Surface ' !i;!-l()] 

CHAPTER  XXVIL— The    Medulla    Oblongata- Lateral     Sur- 
face     102- 1(15 

CIlAl'TKR   XW'III.— 'J'li<.     Medulla     obl.ingafa- Dorsal     Sur- 
face      ](),;  108 

(  IIAI'TKR    XXIX.-The    K.-uilli    \<ul  ride lid  II;! 


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in  2010  witii  funding  from 
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http://www.archive.org/details/anatomyofbrainmaOOburk 


LIST  OF^ILLUSTRATIONS. 

Page. 

PLATE  I.— Dorsal  area  of  Sheep's   Skull 119 

PLATE  II.— Lateral   area   of  Sheep's    Skull 121 

PLATE  III.— Dorsal  Aspect  of  Dura  Matei- 12:3 

PLATE  IV. — Arteries  on  Ventral  Surface  of  the  Brain 12.3 

PLATE  v.— Dorsal   Surface  of  the  Brain 127 

PLATE  VI.— Lateral   Surface  of  the  Brain 129 

PLATE  VII.— Ventral   Surface  of  the  Brain 131 

PLATE  VIIL— Mesial   Surface  of   the   Brain 13:5 

PLATE  IX.— Anterior  Surface  of  the  Briin 13.5 

PLATE  X — Extensioji     of     Cerebrum     to     Show     iJr.iy     and 

White   Matter    137 

PLATE  XL — Corpus  Callosum — Dorsal  Surface 139 

PLATE  XII. — Corinis    Callosum — Showing     Radiating     Fibres 

of    the    Splcnium 141 

PLATE  XIII. — Lateral   Ventricles   of  the   Brain 143 

PLATE  XIV.— Third  Ventricle  and  Choroid  Plexus 145 

PLATE     XV. — Lateral  and  Third  Ventricles  of  the  Brain...  149 

PLATE  XVI. — Fornix,  Hippocampus,  and  Cingulum  Inferior  14!» 
PLATE  XVII. — Fascia    Dentata    and   Mesial    Surface    of   the 

Hippocampus     151 

PLATE  XVIIL— Corpus    Striatum     150 

PLATE  XIX. — Anterior    Commissure    155 

PLATE  XX.— Pillars   of   the   Fornix 157 

PLATE  XXI. — Proximal  Termination  of  Optic   Tract 159 

PLATE  XXII.— The  Corona  Radiata 101 

PLATE  XXIII. — Ventral    Surf  ae  •  of    Pons,  Trapezium,    and 

Medulla    Oblongata    Hi3 

PLATE  XXIV.— Lateral     Surfa-e     of     Cms     Cerebri,     Pons. 

Trapezium,   and  ]\Iedulla  Oblongata I«i5 

PLATE  XXV.— Dorsal      Surface      of      Pons,      and      Medulla 

Oblongata    167 

I'lvA'i'J"]  XXVI.— -Fig.    1.    Coronal    Section   through    Olfactory 

Bulbs.      Fig.    2.    Section    Througli    Anterior    Portion    of 

Lateral   Ventricles    169 

PLATE  XXVri. — Fig.    1.    Section   .lust   Posterior   to   Fissure 

of    Sylvius.      Fig.    2.    Section    through    Substantia    Inter- 

mrjilia     171 


6  ANATOMY    OF    THE   BRAIN 

PLATE  XXVIII. — Fig.  1.  Section  tlirougli  the  Corpus  Pine- 
ale.  Fig.  2.  Section  2.-5  mm.  Anterior  to  Posterior  Ex- 
trenrity  of   Cerebrum    1~3 

PLATE  XXIX. — Sections     tlirougli     the     Collieulus     Superior 

and   Crura   Cerebri    175 

PLATE  XXX. — Sections  through   the  Pons   and  Trapezium..         177 

PLATE  XXXI. — Sections    through    the   Medulla   Oblongata .  .         179 

PLATE  XXXII. — Sections    througli    the    IMedulla    Oblongata 

and    Spinal    Cord 1^1 

PLATE  XXXIII. — Enlarged    Section    of    Spinal    Cord    .5    cm., 

Caudad  to  :\Iodulla  Oblongata 183 

PLATE  XXXIV. — Section  through  tiie  Lower  Portion  of 
Medulla  Oblongata  Showing  Decussation  of  Pyramidal 
Fibres     185 

PLATE  XXXV. — Section    through    Xuclel    Areuati 187 

PLATE  XXXVI.— Section    througli    Caudal    Third    of    Fourth 

Ventricle     189 

PLATE  XXXVII. — Section   through    Trapezium   Cochlear   and 

Vestibular  Nuclei    191 

PLATE   XXXVIII. — Section    Ihroiigh    Colliculi    Superiores  .  .  .         193 

PLATE  XXXIX. — Base   of    Skull    Showing   Dura   Mater   with 

Exits  of  Cranial  X'erves    195 

PLATE  XL.— Base  of   Skull    197 


ANATOMY    OP    THE    BRAIN 


PREFACE. 


It  may  seem  an  unwarranted  liberty  to  ask  the  student 
to  add  this  little  volume  to  his  already  overcrowded 
library,  but  after  the  contents  have  been  carefully  ex- 
amined, I  trust  the  intrusion  will  be  pardoned. 

I  feel,  as  1  think  all  teachers  of  anatomy  do,  that  the 
teaching  of  the  architecture  of  the  human  brain  has  been 
a  failure  for  the  average  medical  student,  not  because  of 
a  want  of  many  very  admirable  works  on  the  subject, 
both  descriptive  and  practical,  but  on  account  of  the 
great  scarcity  of  appropriate  laboratory  material,  or  per- 
haps the  proper  appreciation  of  the  material  ready  at 
hand.  That  neurology  can  be  intelligently  taught  by 
any  other  than  the  laboratory  inethod,  no  teacher  has 
the  hardihood  to  affirm. 

In  looking  up  the  matter  of  anatomical  material  suit- 
able for  the  present  requirements  of  laboratory  work  in 
neurology,  the  sheep  {ovis  aries)  was  found  to  offer  an 
inexhaustible  supply,  and  a  source  easily  reached.  This 
material  can  be  procured  as  fresh  as  need  be,  and  at  a 
cost  quite  within  the  reach  of  anj^  institution  or  indi- 
vidual. 

Its  adaptability  for  the  teaching  of  the  anatomy  of  the 
brain  to  the  medical  student  was  ascertained  by  the  dissec- 
tion of  a  number  of  sheep  brains,  and  by  writing  an  out- 
line of  description  as  a  guide  to  the  student  for  laboratory 
work.  This  outline  was  mimeographed  and  each  student 
was  supplied  with  a  copy  and  with  three  sheep  brains, 
two  of  which  were  removed  while  the  third  was  left  in 
the  brain  case.  The  student  then  worked  out  each  dis- 
.section  as  outlined  and  made  drawings  of  his  preparations. 
The  experiment  was  an  uncjualified  success,  and  removed 
all  apprehension,  so  far  as  the  neurological  laboratory  was 
concerned,  in  the  matter  of  working  material. 

At  the  suggestion  of  Professor  Donaldson  of  the  Uni- 
versity of  Chicago,  I  undertook  the  elaboration  of  my  first 
descriptifm,  and  the  result  is  contained  in  the  following 
pages. 


8  ANATOMY   OF    THE   BRAIN 

This  small  effort  is  of  necessity  very  imperfect,  as  little 
literature  is  available  for  reference;  but  the  writer  trusts 
that  it  may  assist  in  some  measure  those  who,  like  himself, 
are  compelled  to  conduct  a  course  on  the  brain,  and  who 
are  in  need  of  material  or  a  laboratory  guide. 

The  Basel  association  nomenclature  (BNA)  has  been 
followed  as  closely  as  possible.  The  association  name, 
where  it  is  thought  necessary,  is  followed  by  the  common 
or  popular  names  in  parenthesis ;  this  facilitates  the  con- 
sultation of  other  works  on  the  subject.; 

For  a  like  reason  the  following  terms  are  employed: 

Cephalad   (anterior  or  toward  the  head). 

Caudad  (posterior  or  toward  the  tail). 

Ventrad  (ventral  or  toward  the  under  parts). 

Dorsad  (dorsal  or  toward  the  upper). 

Mediad  (median  or  toward  the  middle  line)  and 

Laterad  (lateral  or  toward  the  side). 

The  terms  ventral,  dorsal,  etc.,  are  used  as  being  more 
in  conformity  with  the  spirit  of  the  "BNA"  than  the 
terms  anterior,  posterior,  superior  and  inferior. 

The  drawings,  with  the  exception  of  plates  I  and  II, 
which  are  photographs,  are  the  work  of  the  author ;  they 
were  made  from  dissections,  and  unless  otherwise  indicated 
represent  the  actual  size  of  the  structures  under  con- 
sideration. 

Perhaps  the  only  inconsistency  in  the  work  is  the  sub- 
division of  the  substantia  alba  and  the  substantia  grisea 
of  the  medulla  spinalis  (spinal  cord)  into  tracts  and  col- 
umns somewhat  after  the  manner  in  which  Toldt  arranges 
them  in'  the  human  medulla  spinalis;  and,  furthermore, 
this  arrangement  is  illustrated  by  means  of  an  histological 
preparation,  a  departure  from  the  original  idea  of  the 
work  that  could  not  well  be  obviated.  Histology,  path- 
ology and  embryology  may  prove  this  arrangement  to  be 
at  variance  with  the  truth,  but  until  such  evidence  is  forth- 
coming, the  description  here  given  will  be  helpful. 

The  close  correspondence  between  the  encephalon  of  the 
sheep,  and  that  of  man,  is  a  powerful  argument  in  favor 
of  a  like  correspondence  obtaining  in  the  medullae  spinal es 


ANATOMY   OF    THE   BRAIN  M 

of  the  two  Species.  Even  a  microscopic  examination  of 
some  of  the  tracts  of  the  medulla  spinalis  of  the  sheep 
and  their  course  eephalad  reveals  the  fact  that  their  courses 
are  not  dissimilar  to  those  taken  by  corresponding  tracts 
of  the  human  medulla  spinalis. 

It  has  been  deemed  advisable  to  confine  this  work  to 
the  consideration  of  such  structures  as  can  be  identified 
by  gross  dissection,  using,  as  occasion  may  require,  a 
small  hand  magnifier  or,  preferably,  an  ordinary  dissect- 
ing microscope.  There  are  no  structures  described  or  il- 
lustrated, except  the  medulla  spinalis,  that  cannot  be 
worked  out  by  a  first  year  student  of  ordinary  intelligence. 

The  dissections  from  which  the  illustrations  for  this 
book  were  made  are  now  in  the  museum  of  the  depart- 
ment of  neurology  of  the  University  of  Chicago. 

My  thanks  are  due  Professor  Donaldson  for  many  valu- 
able suggestions  in  the  selection  of  dissections  for  draw- 
ing and  for  much  assistance  in  properly  naming  various 
tracts,  fissures  and  gyri.  Acknowledgment  is  also  due  Dr. 
A.  G.  Wippern  for  assistance  in  arranging  the  nomencla- 
ture. 

Thanks  are  aspecially  due  the  publishers  of  this  vol- 
ume for  the  great  care  they  have  exercised  in  its  produc- 
tion, particularly  on  account  of  the  fidelity  with  which 
they  have  reproduced  the  original  drawings.  The  cuts, 
as  shown  in  the  following  pages,  speak  for  themselves. 

I  wish  to  make  special  acknowledgment  to  Messrs.  Ar- 
mour &  Co.  for  the  very  liberal  manner  in  which  they 
supplied  me  with  material  and  for  permitting  me  to  collect 
such  as  best  suited  my  purpose. 

J.  F.  B. 

108  N.  State  St.,  Chicago. 


ANATO-MY    OP    THE    BRAIN  H 


PREFACE  TO  THE  SECOND  EDITION. 

Iininediately  aftei-  the  publication  of  the  first  edition  of 
this  laboratory  introduction  to  the  study  of  neurological 
anatomy,  the  author  began  the  preparation  of  a  serial  sec- 
tion of  the  bi'ain-steni  of  the  sheep,  stained  by  the  Pal- 
Weig'art  method.  This  piece  of  research  was  due  to  the 
desire  on  the  part  of  the  writer  to  substantiate  his  convic- 
tion.s.  that  the  i-ehitionships  of  the  components  of  the  brain- 
stem of  the  sheep  would  prove  as  useful  in  teaching  the 
architecture  of  the  corresponding  region  of  the  human 
])rain,  as  the  grosser  parts  have  been.  That  this  is  true 
can  be  convincingly  affirmed,  by  comparing  i)lates  XXXII 
to  XXXVIII,  inclusive,  of  the  present  edition,  with  illustra- 
tions of  the  analoLiiuis  regions  of  the  human  brain,  that 
may  be  found  in  any  authoi'itative  work  on  descriptive 
human  anatom.w 

The  wonderfull\'  siiiii)lc  figure  showing  the  cochlear  and 
vestil)ular  nerves  and  their  nuclei,  as  seen  in  plate 
XXXVII,  is  positively  diagi'amatic  in  its  clearness,  and 
yet  this  comi)le.\  mechanism  is  thus  perspicuously  shown 
in  the  space  of  a  half  dozen  sections. 

The  original  idea,  that  the  book  should  contain  the  de- 
scription of  no  sti'uctui-e  tliat  could  not  be  seen  by  a  hand 
glass  or  dissecting  iiiici'osco|)e,  has  been  strictly  followed 
in  the  second  edition.  Most  of  tlie  minute  structures  that 
are  mentioned,  however,  such  as  those  that  occur  in  the 
stained  .sections  of  the  brain-stem,  can  be  seen  with  the  un- 
aided eye.  Moreover,  many  of  these  :;tructures  can  be 
identified  in  unstained  sections  without  an  immoderate 
exertion  of  the  imagination.  For  demonsti-ations  of  this 
character,  sections  should  ])e  cut  as  thin  as  i)0ssible  under 
water,  using  a  sharj)  thiu-bhide  i-a/oi-,  and  placing  the 
specimen  on  parafined  coi-lc  or  dissecting  wa.x.* 

One  gratifying  result  that  may,  in  a  measure,  be  attrib- 
uted to  this  laboratory  guide,  is  the  incentive  it  has  given 
to  the  study  of  iiustaiiicd  se<'1ioiis  of  bi-iiu  tissue.     S])ecific 


12  ANATOMY    OP    THE   BRAIN 

directions,  that  will  very  materially  facilitate  tliis  method 
of  study,  are  given  in  the  text. 

Furthermore,  we  cannot  insist  too  forcibly  upon  the  tear- 
ing process,  in  facilitating  the  dissection  of  the  brain. 
The  study  of  the  larger  bundles  of  fibres  is  greatly  aided 
by  this  method  of  work.  When  the  sheep's  brain  is  used 
as  a  source  of  laboratory  supply,  there  is  no  reasonable 
necessity  for  being  inordinately  sparing  of  brains ;  and  the 
student,  if  permitted  to  use  the  necessary  material,  will 
very  soon  acquire  a  true  and  lasting  perspective  of  this 
intricate  organ. 

Henle  made  frequent  use  of  this  tearing  process  of  dis- 
secting the  human  brain  as  shown  in  Vol.  3  of  his  human 
anatomy  published  in  1868.  We  are  not  paying  sufficient 
attention  to  these  so-called  primitive  methods  in  this  day 
and  age  of  complicated  laboratory  and  often  unsatisfactory 
technie,  and  we  and  our  students  are  the  losers  thereby. 

Thanks  are  due  Professor  Herrick  of  the  University  of 
Chicago  for  suggesting  the  introduction  of  figs.  D.  and  E., 
which  show  more  clearly  than  the  original  plates  the  for- 
amen interventriculare  and  the  attachments  of  the  pia  and 
arachnoid  to  the  dorsal  surface  of  the  medulla  oblongata. 
Thanks  are  due  Dr.  Wippern  for  his  care  in  correcting  the 
proofs.  And  again,  my  thanks  are  due  to  the  publishers 
for  the  accuracy  with  Avhich  they  have  reproduced  my 
original  drawings. 


*Preparation    of    Dissecting    Wax.      Formula: 

Bees    wax     (white    or    yeUow) 4  oz. 

Parafin    (50°)    4   oz. 

Colophonium     1   oz. 

Canada    Balsam    %    oz. 

mix. 
Place  the  ingredients  in  the  desired  container  and 
melt.  Stir  while  cooling  until  the  mixture  begins 
tO'  congeal  on  the  sides  of  the  vessel;  then  allow  to 
stand  in  a  cool  place.  Do  not  allow  the  bottom 
of  the  dish  to  get  cold  too  quickly.  Let  the  mass 
get    quite    cold    before    using. 

If  a  black  mass  is  desired,  add  a  tablespoonful 
of   lamp   black. 

Commercial  rosin  should  not  be  substituted  for 
colophonium. 

This  mass  does  not  shrink,  crack,  not  get  brittle; 
neither  is  it  effected  by  cold.  It  is  very  tenacious 
to  the  dish  and  dissecting  pins. 


ANATOMY    OP    THE    BRAIN  13 

INTRODUCTION. 

During  the  last  few  years  increasing  emphasis  has  been 
laid  on  the  study  of  the  brain  as  a  part,  of  the  anatomical 
training  of  students  preparing  for  medicine. 

In  many  places  where  this  preparatory  work  has  been 
introduced,  human  brains  are  difficult  to  obtain,  and  for 
this  reason  mainly,  the  study  of  this  organ  is  limited  to  a 
few  demonstrations. 

It  may  be  assumed  that  for  some  years,  at  least,  it  will 
not  be  possible  to  relieve  the  difficulty  arising  from  the 
scarcity  of  human  material.  Under  these  circumstances, 
it  seemed  desirable  to  prepare  a  description  of  a  bram  of 
moderate  size,  which  might  be  used  in  place  of  the  human 
brain,  thus  allowing  the  student  to  have  the  entire  speci- 
men under  examination,  and  study  it  at  his  leisure.  This, 
of  course,  is  by  no  means  a  new  idea,  since  the  work  m  the 
Zoological  Laboratory  at  Cornell  University  under  Pro- 
fessor Burt  G.  Wilder  has  for  years  been  conducted  on  this 
principle,  and  furthermore  he  has  there  used  the  sheep's 
brain  for  the  purposes  of  dissection. 

All  things  considered,  there  is  no  more  accessible  mate- 
rial of  the  proper  size  than  the  brain  of  the  sheep,  and 
for  the   purpose   of  utilizing  this,   the  present  book  has 

been  prepared. 

The  directions  for  the  study  of  the  specimen  assume 
that  it  is  the  purpose  of  the  student  to  obtain  a  good 
three-dimensional  impression  of  the  brain  with  which  his 
topographical  terms  may  be  associated.  This  is  much 
facilitated  where  the  text  and  figures  apply  directly  to  the 
specimen  in  hand,  and  it  therefore  seemed  worth  while 
to  brin-  together  the  accompanying  drawings,  explained 
by  a  brief  text,  in  a  form  where  they  could  be  used  in 
connection  with  the  laboratory  work. 

The  chief  dit¥erence  between  the  brain  of  the  sheep  and 
that  of  man  is,  apart  from  size,  first  in  the  cranial  liex- 
nvo  which  is  much  less  developed  in  the  sheep;  second, 
in  the  relative  size  of  the  cerebellar  hemisphere ;  and  third, 
in  the  propo.tional  development  and  sculpturing  of  the 
cerebral  hemispheres.     Ml  of  th.-se  differences  are  readily 


14  ANATOMY    OP    THE   BRAIN 

appreciated  by  the  inspection  of  demonstration  specimens 
or  figures  representing  them. 

On  the  other  hand,  the  student's  greater  difficulties  arise 
in  the  attempt  to  understand  the  deeper  lying  parts  rep- 
resented by  the  inter-brain  and  mid-brain,  together  with 
the  ventricular  cavities.  To  comprehend  these,  careful  dis- 
section is  required,  and  this,  fortunately,  can  be  just  as 
well  carried  out  on  the  brain  of  the  sheep  as  on  that  of 
man. 

It  will  be  seen  from  turning  the  pages,  that  most  of 
the  appearances  described  in  the  text  can  be  observed  with 
the  unaided  eye,  and  the  statements  have  been  so  formu- 
lated as  to  guide  the  student  in  making  his  own  observa- 
tions rather  than  to  present  him  with  a  comprehensive  ac- 
count of  the  several  structures. 

This  book  meets  a  need  that  has  been  felt  for  some 
years,  and  if  at  the  same  time  arrangements  can  be  made 
with  the  firms  dealing  in  sheep  to  remove  the  brains  and 
supply  them  to  laboratories  at  reasonable  prices,  one  me- 
chanical difficulty  standing  in  the  way  of  the  study  of 
the  brain  will  have  been  removed. 

It  is  as  an  aid  to  this  end  that  Dr.  Burkholder  has  pre- 
pared the  following  description  of  the  figures  of  the  sheep's 
brain,  all  of  which  were  draAvn  by  himself  from  his  own 
careful  dissections. 

Henry  H.  Donaldson. 
The   Wistar    Institute    of    Anatomy    and    Biology,    Phila- 
delphia, Pa. 


ANAT()^rV    OF    THE    BRAIN  15 


CHAPTER  I. 
THE  BRAIN-ITS  REMOVAL  AND  PREPARATION. 

THE  ENCEPHALON  OF  THE  SHEEP    {ovis  (Ivies) . 

The  encephalon  (brain)  consists  of  four  large  subdi- 
visions : 

Cerebrum, 

Cerebei.lum, 

Pons,  and 

Medulla  Oblongata; 
all  inclosed  within  the  cranial  cavity,   the  walls  of  which 
in  the  adult  are  osseous,  and  the  sutures  of  the  calvarium 
obliterated. 

To  remove  the  encephahm  ^\'ith()ut  iujuiy  to  its  cover- 
ings or  the  nervi  cerebrales  requires  care,  as  laceration 
of  these  structures  may  lead  to  erroneous  conceptions,  or 
at  least  endanger  a  proi^er  conception  of  the  normal  re- 
lations. 

The  following  instruments  ai-e  necessary  for  dissecting: 
a  large  and  a  small  bone  forceps,  a  brain  knife,  small  scis- 
sors, scalpel,  and  a  pair  of  dissecting  forceps  with  sharp 
points;  all  of  which  must  be  of  good  quality  and  in  prime 
condition.  Nothing  is  more  disastrous  to  good  dissecting 
than  poor  instruments  in  poor  condition. 

Begin  with  the  bone  forceps  at  the  cephalic  extremity  of 
the  cranium  just  behind  the  frontal  edge  of  the  orbital 
fossae  (Plates  I  and  II  A).  The  first  incisions  will  open 
the  large  frontal  sinuses,  the  inner  walls  of  which  form  the 
outer  walls  of  the  brain-case. 

AVorking  caudad,  clip  away  small  portions  of  bone  until 
an  opening  is  made  and  the  outer  covering  of  the  en- 
cephalon is  reached.  Proceed  now  with  the  greatest  care; 
with  the  handle  of  the  scalpel,  pry  the  dense  white  mem- 
brane "the  dura  mater"  away  from  the  skull  before  fur- 
ther clipping  away  the  bone,  a  small  portion  at  a  time. 
Unless  this  precaution  is  taken  this  membrane  will  surely 
be  lacerated. 


16  ANATOMY   OF   THE   BRAIN 

It  will  be  noticed  that  the  dura  mater  is  more  firmly  at- 
tached to  the  inner  surface  of  the  skull  along  the  middle 
line  than  at  the  sides,  while  the  locations  where  the  at- 
tachment is  greatest  will  be  seen  to  be  at  the  sutures  or 
seams  between  the  ossa  cranii. 

Remove  the  calvarium  as  far  caudad  as  the  sutura  lamb- 
doidea  (Plate  IB),  which  separates  the  os  parietalis  from 
the  OS  occipitale;  then  proceed  from  the  foramen  occipitale 
magnum — out  of  which  passes  the  medulla  spinalis — clip- 
ping away  the  condyli  occipitales,  and  finally  the  remain- 
the  portion  of  the  os  occipitale.  Note  how  tightly  the  dura 
clings  to  the  cephalic  portion  of  the  bone,  particularly  at 
the  sutura  lambdoidea.  In  clearing  away  the  lateral  walls 
of  the  brain-case,  caution  must  be  exercised  not  to  lacerate 
the  nervi  cerebrales. 

For  the  student  of  human  anatomy  preparing  for  the 
study  of  medicine,  a  further  use  of  the  skull  can  be  made 
for  the  purpose  of  getting  an  idea  of  the  arrangement  of 
the  internasal  bones,  and  the  distribution  of  the  Nn. 
olfactorii.  Remove  the  nasal  bones  by  means  of  the  bone 
forceps,  and  a  veritable  labyrinth  of  convoluted  bony  struc- 
tures will  be  exposed.  These  are  the  turhinal  hones  (con- 
chae  etJimoideales)  or  the  ethmoturhinals. 

The  Nn.  olfactorii  can  be  traced  for  some  distance,  by 
using  a  reasonable  amount  of  care,  showing  their  distribu- 
tion to  the  Schneiderian  membrane  covering  the  superior 
turbiual  bones.  This  dissection  requires  very  little  skill, 
and  consumes  a  modicum  of  time. 


ANATOMY    OP    THE    BRAIN  17 

CHAPTER  II. 

THE  COVERINGS  OF  THE  BRAIN. 

Having:  removed  the  brain-case,  a  drawing  should  be 
made  of  the  exposed  dura,  of  the  Sinus  Sagittalis  (longi- 
tudinal sinus),  the  Sinus  Transversus  (lateral  sinus),  and 
the  CoNFLUENS  Sinuum  (Torcular  Herophilii),  exposed  as 
directed  in  the  description  of  the  dura  mater,  and  shown 
in  Plate  III. 

The  student  may  now  proceed  in  one  of  two  ways ;  either 
the  dura  can  be  Avholly  reflected  and  the  encephalon  re- 
moved and  placed  in  a  ten  per  cent  solution  of  formalin,  or 
a  long  incision  may  be  made  over  each  cerebral  hemisphere 
through  the  dura  and  the  whole  skull  with  the  attached 
brain  placed  in  the  solution.  In  either  case  it  must  remain 
in  a  solution  of  this  strength  for  four  or  five  days,  and 
then  be  kept  in  a  five  per  cent  solution  as  long  as  required 
for  dissection  and  study. 

In  removing  the  encephalon,  proceed  from  the  caudal  ex- 
tremity, clipping  away  the  nervi  cerebrales  close  to  the 
foramina  through  Avhich  they  pass  (Plates  VII  and 
XXXIX),  preserving  at  least  1  cm.  of  the  nervi  optici,  and 
taking  care  to  remove  the  whole  of  the  bulbi  olfactorii  from 
their  fossae;  be  particularly  careful  with  the  N.  facialis  and 
the  N.  acusticus. 

Each  time  the  brain  is  to  be  studied  it  should  be  placed 
in  water  for  an  hour  to  remove  the  formalin.  This  proced- 
ure obviates  the  irritation  of  the  conjunctiva  and  respira- 
tory mucous  membranes,  which  the  vapor  of  formalin  will 
cause  if  allowed  to  circulate  through  the  laboratory. 

MENINGES. 

These  membranes  surround  the  encephalon  for  its  pro- 
tection and  partial  nourishment.  There  are  three  of  thein, 
and  from  without  inward  are  called: 

Dura, 

Arachnoid,  and 

1»IA. 


18  ANATOMY   OF   THE   BRAIN 

The  dura  is  the  first  exposed  on  removing'  the  calvarium, 
the  pia  is  closely  attached  to  the  encephalon,  and  the 
arachnoid  lies  between  the  two. 


ANATO:»[V    OP    THE    BRAIN  19 


CHAPTER  III. 


DURA  MATER  ENCEPHALI. 
(dura,  hard;  mater,  a  mother.) 
The  dura  (Plate  III)  is  the  strongest  of  the  three  mem- 
branes, and  not  only  protects  the  encephalon,  but  by  send- 
ing projections  from  its  inner  surface,  between  the  hemi- 
sphaeria  cerebri  and  between  the  cerebrum  and  the  cere- 
bellum, acts  as  a  support.  This  membrane  consists  of  white 
fibrous  tissue  arranged  in  bundles  or  strands  that  run  in 
many  different  directions. 

Over  the  hemisphacria  cerebri,  vermis  cerebelli  and  hemi- 
sphaeria  cerebelli,  it  is  quite  thin  and  cannot  be  separated 
into  distinct  layers.  The  thickest  and  densest  part  of  the 
membrane,  as  previously  mentioned,  lies  directly  beneath  the 
sutura  sagittal  is  and  the  sutura  lambdoidea.  At  the  cephalic 
extremity  there  is  a  triangular  thickening  consisting  of  two 
of  three  layers;  the  apex  of  this  triangle  points  caudad  in 
the  middle  line,  tlu^  base  ccphalad  and  ventrad  into  the 
cephalic  extremities  of  the  fos.sae  olfactoriae.  The  gyri, 
and  sulci  cerebri  can  be  seen  somewhat  indistinctly  through 
the  thinner  parts  of  the  membrane. 

The  dura  consists,  roughly  speaking,  of  two  layers,  an 
outer  and  an  inner,  the  foi-mer,  constituting  the  endosteum 
of  the  ossa  cranii,  is  very  fii-mly  attached  to  the  inner  sur- 
faces of  the  cranium,  and  particularly  so  at  the  sutures,  into 
which  fibrous  bands  <if  dura  pass.  Between  this  layer  and 
the  bone  is  a  large  number  of  arteries  of  various  sizes,  called 
the  arteriac  meningeae,  which  supply  the  dura  and  the 
inner  table  of  the  ossa  cranii.  This  outer  layer  of  the  dura 
also  gives  off  tubuhn-  prolongations  which  surround  the 
nervi  cercbralcs  as  they  pass  through  the  various  foramina ; 
that  accompanying  the  nervus  opticus  divides  as  the  nerve 
emerges  from  the  foramen  opticum,  into  its  two  primary 
layers,  the  inner  continuing  as  a  sheath  for  the  nerve  form- 
ing its  cpincufium,  while  the  outer  unites  with  the  peri- 
osteum of  the  fossa  orbitalis. 


20  ANATOMY    OP    THE    BRAIN 

The  inner  layer  of  the  dura  as  it  lies  over  the  fissura 
longitudinalis  cerebri,  and  the  fissura  transversa  cerebri, 
leaves  the  outer  layer  and  dips  into  these  fissures.  That 
which  rests  in  the  fissura  longitudinalis  cerebri  is  called 
the  falx  cerebri,  very  slightly  developed  in  the  sheep ;  that 
in  the  fissura  transversa  cerebri  is  the  tentorium  cerebelli. 
Where  the  falx  cerebri  and  the  tentorium  cerebelli  leave  the 
outer  layer,  and  in  various  locations  on  the  base  of  the 
cranium,  the  two  layers  of  the  dura  separate  and  leave  large 
spaces  of  various  shapes  called  sinuses,  which  convey  venous 
blood  from  the  encephalon.  These  sinuses,  like  veins,  are 
lined  with  endothelial  cells. 

The  Falx  Cerebri  has  the  shape  of  a  sickle,  hence  its 
name,  and  begins  about  2  cm.  caudad  of  the  cephalic  ex- 
tremity of  the  encephalon  where  it  is  exceedingly  narrow 
and  receives  the  vena  frontalis.  It  widens  as  it  proceeds 
caudad,  and  is  firmly  attached  to  the  sagittal  centre  of  the 
tentorium  cerebelli.  It  is  quite  narrow  even  at  its  widest 
portion  and,  really  is  suspended  between  the  hemisphaeria 
cerebri  only  at  their  caudal  extremities.  The  long  tri- 
angular canal  inclosed  by  the  falx  cerebri  and  the  outer 
layer  of  the  dura  is  called  the  sinus  sagittalis,  analogous  in 
location  to  the  sinus  sagittalis  superior  (superior  longi- 
tudinal sinus)  in  man.  The  flow  of  blood  in  this  sinus  is 
directed  toward  the  caudal  extremity  of  the  encephalon. 

As  the  falx  proceeds  caudad,  numerous  veins  enter  its 
sharp  concave  border  to  empty  blood  into  the  sinus  sagit- 
talis. A  large  vein,  the  V.  cerebri  magna  (vein  of  Galen), 
enters  the  falx  about  &  mm.  cephalad  to  the  tentorium. 
This  vein  conveys  blood  from  the  plexus  chorioideus  of  the 
lateral  and  third  ventricles  and  the  lobi  occipitales  (caudal 
extremities  of  the  hemispheres). 

The  Tentorium  CEREBELiii,  the  other  reflection  of  the 
inner  layer  of  the  dura,  forms  a  partial  roof  over  the  fossa 
cranii  posterior.  This  layer  or  tent  is  membraneous  in 
the  sheep  and  in  man ;  but  is  osseous  in  some  species,  as 
the  cat,  dog,  lion.  As  you  follow  the  falx  cerebri  caudad 
and  ventrad  it  suggests  the  parting  of  the  falx  into  halves 
which  gradually   diverge,  leaving  a  large,   somewhat  tri- 


ANATOMY   OF    THE    BRAIN 


21 


angular  opening,  through  which  passes  the  mesencephalon, 
composed  of  the  structures  connecting  the  cerebrum  with 
the  cerebellum,  pons,  and  medulla  oblongata. 

The  inner  margins  of  the  tentorium  are  thus  free,  while 
its  outer  borders  are  attached  to  the  outer  layer  of  the  dura 
lining  the  cranium.  The  free  margin  is  thin,  but  where  the 
structure  is  attached  to  the  outer  dura  it  is  very  thick,  and 
at  the  point  where  the  falx  meets  the  tentorium  will  be 
found  a  large  triangular  thickening  in  the  outer  portion  of 
which  rests  the  confluens  sinuum. 

Traced  cephalad  along  the  basis  cranii,  the  tentorium  is 
attached  laterally  to  the  external  lip  of  the  sulcus  carotieus 
and  blends  gradually  with  the  dura  lining  the  fossa  cranii 
media  (Plate  XXXIX).  As  the  tentorium  proceeds  ce- 
phalad it  becomes  greatly  thickened,  and  almost  tendonous 
in  character. 

The  sinuses,  as  previously  stated,  are  spaces  between  the 
two  layers  of  the  dura  and  convey  venous  blood. 

The  Sinus  Sagittalis  (Plate  III).  Make  an  incision 
in  the  sagittal  line  of  the  dura  mater  about  4  cm.  from  the 
cephalic  extremity  of  the  encephalon,  and  the  sinus  will  be 
exposed ;  pass  a  bristle  cephalad  as  far  as  possible  without 
using  force,  and  then  dissect  it  out,  and  the  sinus  will  be 
seen  to  end  in  the  V.  frontalis  within  about  2  cm.  of  the 
cephalic  extremities  of  the  lobi  frontales,  which  are  drained 
by  this  vein.  Traced  caudad,  the  sinus  enters  the  con- 
fluens sinuum. 

The  Confluens  Sinuum  is  situated  where  the  falx  and 
the  tentorium  meet,  directly  beneath  the  protuberantia  oc- 
cipitalis externa.  Leading  from  the  confluens  sinuum  at 
each  side  is  a  sinus  transversus  which  follows  for  some  dis- 
tance the  attachment  of  the  tentorium. 

These  sinuses  finally  enter  the  substance  of  the  os  oceipi- 
tale,  through  which  they  run  for  a  short  distance  and  then 
re-enter  the  cranial  cavity  close  to  the  foramina  condyli 
anteriora  where  each  enters  a  large  sinus,  the  sinus  hasilaris 
magna  resting  on  the  os  basilare  (Plate  XL).  This 
sinus  is  wide  ventrad  but  gradually  becomes  smaller  as  it 
passes  dorsad,  the  two  extremities  not  quite  meeting  in  the 


22  ANATOMY    OP    THE    BRAIN 

dorsal  midline.  Pass  a  bristle  along  each  sinus  transversus 
and  dissect  each  out  with  the  bone  forceps.  The  sinus  basi- 
laris  magna  is  drained  by  the  two  venae  vertebrales  that 
leave  the  cranial  cavity  through  the  foramen  occipitale 
magnum,  one  on  either  side  of  the  medulla  spinalis. 

The  large  V.  ophthalmica  enters  the  fossa  cranii  media 
through  the  fissura  sphenoidalis,  bringing  blood  from  the 
orbit  (Plate  XL).  This  vein  enters  the  sinus  cavernosus. 
Each  sinus  cavernosus  rests  in  the  sulcus  caroticus  on 
either  side  of  the  corpus  .sphenoidale. 

Running  almost  completely  around  the  hypophysis  is  the 
sinus  circularis;  on  each  side  this  sinus  communicates  freely 
with  the  sinus  cavernosus. 

The  sinus  circularis  and  the  sinus  cavernosi  contain  a  fine 
reticulum  of  connective  tissue,  arranged  somewhat  after  the 
manner  of  the  cancellous  tissue  in  bone. 

In  each  sinus  caverncsus  will  be  seen  a  very  dense  plexus' 
of  small  arteries,  called  the  rete  mirahile  (Galen)  which 
will  be  described  in  connection  with  the  arterial  circulation 
on  the  ventral  surface  of  the  encephalon. 

As  each  sinus  cavernosus  passes  caudad  it  lies  mediad  to 
the  N.  trigeminus,  the  fibrous  sheath  (epineurium)  of  which 
is  firmly  attached  to  the  external  wall  of  the  sinus. 

Passing  through  the  sinus  cavernosus  are  the  N.  oculomo- 
torius,  N.  trochlearis,  and  the  N.  abducens  on  their  way  to 
the  fissura  sphenoidalis;  the  sinus  cavernosus  empties  into 
the  sinus  petrosiis  inferior  which  runs  along  the  ventral 
border  of  the  pars  petrosa  of  the  os  temporale  and  ends  at 
the  foramen  jugulare  by  entering  the  V.  jugularis  interna. 
A  bristle  should  be  passed  along  the  sinus  petrosus  inferior 
and  dissected  out  by  means  of  the  bone  forceps. 

In  this  connection  a  very  nice  dissection  can  be  made  of 
the  ganglion  semilunare  (Gasseri)  showing  the  origins  of 
the  N.  ophthalmicus,  N.  maxillaris,  and  the  N.  mandibularis. 
The  dissection  should  begin  at  the  fossa  temporalis  and  be 
carried  mediad,  proceeding  carefully  when  the  region  of 
the  sinus  cavernosus  is  reached. 

At  this  stage  the  student  must  cease  operations  on  the 
basis  cranii,  which  are  to  be  resumed  when  working  out  the 


ANATOMY    OF    TlIK    BRAIN  23 

exit  of  the  iiervi  cerebrales  from  the  cranial  cavity.  Per- 
haps the  better  way  to  make  this  latter  preparation  would 
be  to  decalcify  the  basis  cranii  by  immersing  it  in  a  ten  per 
cent  solution  of  commercial  nitric  acid  in  water,  after  which 
the  nervi  cerebrales  can  be  easily  removed  with  the  dural 
processes  surrounding  them. 


24  ANATOMY    OF    THE    BRAIN 


CHAPTER  IV. 
ARACHNOIDEA  ENCEPHALI. 

(ARACHNE,    spider's    WEB;    EIDOS,    LIKE.) 

The  arachnoid  is  a  membrane  of  very  uncertain  quantity 
and  variable  in  its  character  and  distribution.  As  a  rule  it 
covers  the  entire  encephalon  and  lies  immediately  beneath 
the  dura,  and  the  space  between  it  and  the  dura  is  called  the 
cavum  subdurale. 

This  membrane  is  most  easily  identitied  in  the  region  im- 
mediately caudad  to  the  cerebellum,  where  the  dura  and 
the  arachnoid  are  reflected  from  the  vermis  to  the  dorsal 
surface  of  the  medulla  oblongata;  as  a  rule  the  membrane 
is  continued  as  a  tubular  prolongation  over  the  medulla  ob- 
longata thence  to  the  medulla  spinalis. 

The  space  beneath  the  arachnoid  is  the  cavum  suharach- 
noideale,  and  at  certain  places  this  space  is  quite  deep,  as  in 
the  angle  made  by  the  cerebellum  with  the  medulla. 

At  the  fossa  interpeduncularis,  and  other  limited  places, 
these  deep  spaces  are  called  the  cisternae  subarachnoideales, 
and  are  filled  with  a  very  delicate  reticulum  of  tissue  which, 
like  all  the  spaces  between  the  arachnoid  and  the  pia,  con- 
tains the  cerebro-spinal  fluid. 

The  reticulum  forms  the  trabeculae  subarachnoidealae. 
Place  a  small  quantity  on  a  slide  in  glycerine  and  water; 
tease  under  a  dissection  microscope,  and  study.  Clip  a 
small  piece  of  arachnoid  from  that  covering  the  hemisphae- 
rium  cerebri ;  mount  in  glycerine ;  it  will  present,  mingled 
with  a  few  elastic  fibres,  a  very  fine  reticulum  of  white 
fibres  which,  under  a  dissecting  microscope,  looks  like 
ground  glass.  Under  a  higher  power  a  very  beautiful 
plexus  of  capillaries  and  arterioles  can  be  seen,  many  of 
them  containing  blood.  A  large  number  of  arteries  can 
be  seen  passing  through  the  trabeculae  subarachnoidealae, 
but  the  tissue  itself  is  nonvascular.  The  trabeculae  are 
most  abundant  on  the  ventral  surface  of  the  encephalon 
and  contain  much  fluid  which  acts  as  a  water-bed  for  the 


ANATOilY    OP    THE    BRAIN  25 

organ  it  supports;  while  over  the  convexities  of  the  hemis- 
phaeria  cerebri  the  flnid  is  very  scarce,  thouj^rh  more  abun- 
dant beneath  the  portions  of  arachnoid  that  lie  over  the 
sulci  cerebri. 


2G  ANATOMY    OF    THE   BRAIN 


CHAPTER  V. 
PIA  MATER  ENCEPHALI. 

(PIA^    TENDER;    MATER,    A    MOTHER.) 

The  pia  mater  is  an  exceedingly  thin  membrane  in  con- 
tact with  the  encephalon;  and  containing  vessels  in  large 
quantity,  it  provides  nutrition  for  the  entire  substance  of 
the  brain  cortex. 

This  delicate  membrane  dips  to  the  bottom  of  the  various 
sulci  and  during  the  development  of  the  organ  is  pushed 
through  the  fissura  transversa  cerebri  (great  transverse 
fissure)  into  the  ventricular  cavities  of  the  encephalon, 
where  it  will  be  further  studied,  when  describing  those 
spaces. 

At  the  cephalic  extremity  of  the  encephalon  there  is  in  the 
cells  of  the  pia  a  deposit  of  pigment  granules  which  in  some 
instances  assumes  the  form  of  a  large  triangular  patch,  ly- 
ing beneath  the  similarly-shaped  thickening  of  the  dura. 
This  deposit  of  pigment  is  black  and  may  be  scattered  in 
various  other  locations,  notably  on  the  ventral  surfaces  of 
the  lobi  frontales.  In  some  encephala  this  pigment  will 
be  found  as  far  caudad  as  the  medulla  spinalis.  Animals 
killed  at  different  seasons  of  the  year  do  not  show  any 
regular  variation  in  the  quantity  or  the  extent  of  dis- 
tribution of  this  pigment;  but  from  the  limited  number 
of  specimens  examined,  it  appears  to  be  much  less  in 
lambs  under  one  year  than  in  adult  sheep. 

Toward  the  caudal  extremity  of  the  medulla  oblongata, 
the  pia  is  greatly  increased  in  density  and  thickness  as 
it  becomes  the  pia  of  the  medulla  spinalis.  In  this  location 
two  distinct  layers  can  be  distinguished ;  an  external,  whose 
fibres  run  longitudinally,  and  an  inner  with  transverse 
fibres,  the  latter  appearing  to  be  the  more  numerous.  Ex- 
amine a  small  portion  under  the  dissecting  microscope. 

In  the  region  of  the  medulla  spinalis,  and  the  caudal 
portion  of  the  medulla  oblongata  this  thickened  pia  is 
furthermore  greatly  increased  laterally,  forming  the  liga- 


ANATOMY    OF    THE    BRAIN  27 

inottutn  dniticitldliui} ;  lying  between  the  dorsal  and  ventral 
roots  of  the  Nn.  cerebrales,  and  passing  eephalad,  ventral 
to  the  roots  of  the  N.  aceessoriiis. 

The  lateral  border  of  this  liganieutuni  denticulatmn 
occasionally  takes  the  form  of  a  white  fibrous  cord,  which 
runs  parallel  to  the  spinal  portion  of  the  N.  accessorioiis. 
This  cord  may  be  mistaken  for  a  part  of-  the  nerve,  which 
in  this  neighborhood,  is  occasionally  divided  into  two  well- 
defined  fasciculi,  quite  similar  in  color  and  consistency  to 
the  ligamentous  cord. 

These  ligaments  on  each  side  appear  to  blend  with  the 
dura,  as  it  forms  the  tubes  for  the  exit  of  the  Nn.  glosso- 
pharyngei,  Nn.  vagi,  and  Nn.  accessorii. 

At  the  point  where  the  pia  is  reflected  from  the  caudal 
surface  of  the  cerebellum  to  the  dorsal  surface  of  the  me- 
dulla oblongata,  there  is  occasionally,  a  median  foramen, 
called  the  apertura  mediana  ventriculi  quarti  (foramen  o* 
Magendie). 

If  we  trace  the  pia  a  short  distance  caudad  on  the  medulla 
spinalis,  it  will  be  seen  to  lose  its  excessive  thickness,  and 
becomes  the  delicate  fibro-vascular  membrane  usually  de- 
scribed. 


28  ANATOMY    OF   THE   BRAIN 


CHAPTER  VI. 

BLOOD  VESSELS  AT  THE  BASE  OF  THE  BRAIN. 

The  blood  supply  (Plate  IV)  to  the  encephalon  is  almost 
entirely  derived  through  the  arterid  carotis  interna  on  either 
side.  The  internal  carotid  artery,  after  it  is  given  off  from 
the  common  carotid,  enters  the  cranial  cavity  through  the 
foramen  ovale,  passing  ventrad  to  the  proximal  extremity  of 
the  N.  mandibularis  which  leaves  the  cranial  cavity 
through  the  same  opening.  As  the  artery  enters  the  cran- 
ial cavity  it  lies  opposite  the  caudal  extremity  of  the  fossa 
hypophyseos,  where  it  immediately  divides  into  a  plexus  of 
small  arterioles,  the  rete  mirabile,  which  in  their  turn  simi- 
larly divide,  and  so  on  until  the  whole  of  the  sinus  cavern- 
osus  is  completely  filled  with  small  arteries  in  a  manner 
similar  to  the  arrangement  of  the  vas  aft'erens  in  the  kid- 
ney forming  the  glomerulus  inside  the  capusula  renis.  This 
plexus  of  vessels  also  invades  the  fossa  hypophyseos  occu- 
pying all  the  space  not  taken  by  the  hypophysis  and  sinus 
circularis. 

The  vessels  from  the  two  sides  come  very  close  together 
caudad  to  the  hypophysis,  but  the  arteries  of  one  side  do 
not  anastomose  with  those  of  the  other.  The  small  ar- 
teries are  finally  gathered  together,  opposite  the  centre  of 
the  hypophysis  and  form  one  large  artery  on  each  side,  the 
arteria  propria  cerebri. 

These  pierce  the  dura  which  forms  the  roof  of  the  sinus 
cavernosus  on  either  side  of  the  foramen  diaphragmatis 
sellae  and  at  once  divide  into  two  rami  nearly  opposite  the 
infundibulum,  the  ramus  anterior  passing  cephalad,  and  the 
ramus  posterior,  caudad.  The  former  nins  cephalad  in  the 
sulcus  between  the  tractus  opticus  and  the  lobus  hippo- 
campi ;  it  then  turns  sharply  mediad,  and  in  some  cases  runs 
almost  parallel  with  the  tractus  opticus. 

When  this  anterior  ramus  reaches  the  nervus  opticus  it 
divides  into  two  branches,  the  a.  cerebri  anterior,  con- 
tinuing on  as  the  apparent  extension  of  the  ramus  anterior 


ANATOMi'   OF    THE    BRAIN  29 

to  the  fissura  longitudinalis  cerebri,  and  the  a.  cerebri 
MEDIA  passing  directly  laterad  in  the  fissura  cerebri  later- 
alis (fissure  of  Sylvius).  The  latter  artery  is  widely  and 
irregularly  distributed  to  the  lateral  aspect  of  the  hemi- 
sphaerium  cerebri,  passing  dorsally  in  some  instances  as  far 
as  the  fissura  longitudinalis  cerebri,  supplying  also  a 
considerable  portion  of  the  external  surface  of  the  lobus 
frontalis  and  the  lobus  parietalis. 

The  A.  cerebri  anterior  passes  cephalad  usually  on  the 
ventral  surface  of  the  lobus  frontalis,  and  is  distributed 
to  the  facies  ventralis  and  the  facies  medialis  of  this  por- 
tion of  the  encephalon.  As  the  Aa.  cerebri  anteriores  pass 
cephalad  they  anastomose  at  one  or  more  points,  permitting 
a  free  communication  between  the  vascular  systems  of  the 
two  sides.  At  the  bifurcation  of  the  A.  propria  cerebri,  a 
large  branch  is  usually  seen,  the  A.  cerebri  posterior,  which 
may  arise  either  from  the  ramus  anterior  or  the  ramus  pos- 
terior. It  passes  laterad  and  caudad  across  the  pedunculus 
cerebri  and  is  soon  hidden  by  the  lobus  hippocampi.  It  is 
distributed  to  the  facies  medialis  and  the  facies  ventralis  of 
the  lobus  occipitalis. 

The  rami  posteriores  pass  caudad  and  converge  to  meet 
beneath  the  fossa  interpenduncularis,  where  the  nervi  oculo- 
motorii  (third  pair  of  cranial  nerves)  emerge  from  the 
pedunculi  cerebri  (crura  cerel)ri),  forming  the  arteria  basi- 
laris;  this  artery  runs  directly  caudad  in  the  middle  line  on 
the  ventral  surface  of  the  pons,  and  the  medulla  oblongata. 

As  the  ramus  posterior  reaches  the  N.  oculomotorius  it 
gives  off  a  branch,  the  A.  basilaris  gangliaformis  posterior 
that  passes  laterad,  cephalad  to  the  root  of  the  nerve,  winds 
around  the  pedunculus  cerebri,  and  is  distributed  to  the 
pulvinar,  corpora  geniculata,  and  the  corpora  quadrigemina. 

Just  before  the  rami  unite,  a  large  branch,  the  A.  cerebelli 
anterior  passes  laterad  and  is  distributed  to  the  facies  dor- 
salis  and  thei  facies  lateralis  of  the  cerebellum ;  it  runs 
caudad  in  the  sulcus  between  the  vermis  and  the  hemi- 
sphaerium  cerebelli,  to  anastomose  with  the  artery  next  to 
be  described,  the  A.  cerebelli  posterior. 

This  artery  ai'ises  fniin  the  A.  hasilai-is  as  it  passes  over 


30  ANATOMY    OF   THE   BRAIN 

the  groove  between  the  pons  and  the  medulla  oblongata. 
It  lies  dorsad  to  the  N.  abdueens,  supplies  the  dorsal  and 
lateral  surfaces  of  the  medulla  oblongata  as  well  as  the 
neighboring  parts  of  the  cerebellum ;  it  then  passes  dorsad 
and  cephalad  to  meet  the  A.   cerebelli  anterior. 

On  proceeding  caudad  the  A.  basilaris  gives  off  small 
branches  from  either  side  which  are  distributed  to  the  ven- 
tral surface  and  sides  of  the  medulla  oblongata.  In  the 
region  where  the  medulla  oblongata  merges  into  the  medulla 
spinalis,  the  A.  basilaris  breaks  up  into  a  spray  of  little 
branches  which  are  distributed  to  the  adjacent  parts;  at 
its  caudal  extremity  the  artery  can  be  seen  anastomosing 
with  the  A.  spinalis  ventralis,  which  passes  caudad  through- 
out the  entire  length  of  the  medulla  spinalis. 

There  is  a  very  peculiar  and  useful  arrangement  of  the 
larger  arteries  on  the  ventral  surface  of  the  central  portion 
of  the  encephalon  called  the  circulus  arteriosus  (circle  of 
AVillis).  As  the  Aa.  cerebri  anteriores  approach  the  mid- 
line, just  cephalad  to  the  chiasma  opticum,  they  are  con- 
nected directly  or  indirectly  by  one  or  more  small  arteries 
called  the  Aa.  communicantes  anteriores,  thus  completing 
the  cephalic  portion  of  the  circle,  while  the  caudal  part 
is  formed  by  the  union  of  the  rami  posteriores. 

A  drawing  should  be  made  of  the  ventral  surface  of  the 
encephalon  showing  the  circle,  the  proximal  portion  of  its 
branches,  and  the  other  structures  of  interest.  The  obvious 
functions  of  this  circle  formed  by  the  anastomosis  are  to 
supply  a  constant  quantity  of  blood  to  the  encephalon  in  an 
even  stream,  with  a  like  degree  of  pressure  in  every  direc- 
tion, and  to  insure  a  free  supply  to  the  whole  encephalon, 
should  one  or  the  other  of  the  sources  of  blood  to  the  circle 
be  obliterated. 

The  student  should  bear  in  mind  that  the  formation  of 
the  circulus  arteriosus  of  the  sheep  differs  from  that  of  the 
human  brain,  where  there  is  an  additional  supply  of  blood 
supplied  by  the  large  A  a.  vertebrales. 


ANATOMY    OF    THE    BRAIN  31 


CHAPTER  VII. 
THE  EXTERNAL  SURFACE  OF  THE  BRAIN. 

THE    HEMISPHAERIA    CEREBRI. 

The  heiiiisphaeria  cerebri  are  two  symmetrically  arranged 
portions  of  the  encephalon,  separated  by  the  pissura  longi- 
TUDiNALis  cerebri,  Constituting  its  largest  subdivisions. 

The  outermost  or  ectal  portion  of  each  hemisphaeriura, 
that  which  is  seen  after  the  encephalon  is  cleared  of  its 
meninges,  is  the  pai,lium.  It  is  characterized  by  a  series 
of  long,  narrow  folds,  much  convoluted,  which  have  a  some- 
what definite  and  regular  arrangement. 

The  sagittal  diameter  of  the  cerebrum  is  about  7  cm.,  the 
greatest  transverse  diameter  about  6  cm.,  while  the  dorso- 
ventral  will  average  about  4  cm. ;  these  measurements  vary 
somewhat  in  difiPerent  specimens. 

The  external  layers  of  the  pallium  consists  of  the  cell 
bodies  of  myriads  of  neurones  (nerve  cells)  which  consti- 
tute a  Dart  of  the  substantia  grisea  or  cortex  of  each  hemi- 
sphaerium.  Internal  to  this  substantia  grisea  is  the  sub- 
stantia alba,  composed  principally  of  medullated  fibres  of  . 
the  neurones  (axones  with  their  sheaths).  Make  a  small 
wedge-shaped  incision  into'  one  of  the  gyri  cerebri,  and 
the  differentiation  of  the  cerebral  matter  into  substantia 
grisea  and  substantia  alba  can  be  easily  verified. 

The  following  short  method  of  staining  the  substantia 
grisea  to  show  its  constituent  neurones  can  be  easily  carried 
out.  A  small  quantity  of  substantia  grisea  is  placed  on  a 
coverglass,  and  a  second  cover  glass  placed  directly  on  it 
and  squeezed  down  so  that  the  nerve  substance  is  smeared 
evenly  over  both  glasses.  The  covers  are  then  separated 
and  floated  for  two  hours,  film  downward,  on  a  saturated 
aqueous  solution  of  methylene  blue.  They  are  then  washed 
in  distilled  water  and  dried;  finally,  after  exposure  to  a 
gentle  heat  to  thoroughly  dry  them,  they  are  mounted  in 
bfilsam.* 

♦H.  L.  Osborn,  Journal  of  Applied  Microscopy,  Vol.  1,  p.  7. 


32  ANATOMY    OF    THE   BRAIN 

The  irregular  depressions  on  the  surface  divide  each 
hemisphaerium  into  gross  subdivisions  called  lobi  cerebri, 
and  these  again  into  gyri  cerebri  (cerebral  convolutions). 
The  larger  depressions  are  called  fissures;  those  separating 
the  gyri,  which  are  smaller  are  called  sulci. 

The  layer  of  substantia  grisea  constituting  the  cortex  is 
not  an  homogeneous  mass  of  matter  with  the  neuron  bodies 
arranged  in  a  heterogeneous  manner.  These  neuron  or 
cell  bodies  are  arranged  in  definite  stratae,  which  in  some 
specimens  prepared  by  the  Kaiserling  method,  can  be  faintly 
seen  by  the  unaided  eye. 


ANATOMY   OP   THE   BRAIN  33 


CHAPTER  VIII. 


DORSAL  SURFACE  OF  THE  CEREBRUM. 

On  the  fades  dorsalis  cerebri  (Plates  V  and  IX)  of 
each  hemisphaerium  is  a  transverse  fissure  called  the  fissura 
cruciata.  It  lies  about  2.5  cm.  caudad  to  the  cephalic  ex- 
tremity of  the  encephalon,  is  inclined  slightly  cephalad  as  it 
passes  laterad  and  separates  the  lobus  frontalis  from  the 
lobus  parietalis. 

The  fissura  cruciata  in  some  specimens  does  not  reach 

the  lateral  border  of  the  dorsal  surface,  but  rests  between 

the  caudal  extremity  of  the  gyrus  frontalis  medialis  and 

the   cephalic   extremity   of   the   gyrus  parietalis   externus 

(gyrus  lateralis). 

The  facies  dorsalis  of  the  lobus  frontalis  is  divided  into 
too  well-defined  gyri :  a  mesial,  called  the  gyrus  frontalis 
superior,  and  a  lateral,  the  gyrus  frontalis  medialis. 

These  gyri  are  separated  from  each  other  by  the  sulcus 
coronalis  which  is  really  a  prolongation  of  the  fissura  cru- 
ciata ;  this  fissure  passes  cephalad  in  the  sagittal  plane  and 
terminates  in  a  bifurcation  near  the  polus  anterior.  The 
gyrus  frontalis  superior  is  in  most  cases  somcAvhat  de- 
pressed, particularly  at  its  caudal  extremity,  where  a  well 
marked  notch  appears  which  is  the  cephalic  termination  of 
the  sulcus  splenialis  (Plate  IX).  In  many  specimens  the 
A.  cerebri  media  leaves  the  fissura  cerebri  lateralis  and  con- 
tinues its  course  in  the  fissura  cruciata  to  reach  the  neigh- 
borhood of  the  fissura  longltudinalis  cerebri. 

There  is  another  very  important  and  well  marked  fissure 
situated  on  the  facies  dorsalis  called  the  fissura  suprasylvia. 
This  fissure  begins  on  the  facies  lateralis  cerebri  about  1  cm. 
cephalad  to  the  middle  of  the  fissura  cerebri  lateralis;  it 
then  passes  caudad  and  dorsad  winding  around  the  summit 
of  the  fissura  cerebri  lateralis  lying  about  2.5  cm.  laterad  to 
the  fissura  longltudinalis.  The  further  course  of  the  fissure 
runs  in  a  caudo-laterad  direction,  reaching  in  some  in- 
stances the  tentorial  surface  of  the  lobus  occipitalis.     The 


34  ANATOMY   OP    THE   BRAIN 

caudal  two-thirds  of  the  fissura  suprasylvia  separates  the 
parietal  from  the  temporal  lobie. 

Occasionally  the  lateral  extremity  of  the  fissura  cruciata 
appears  to  pass  directly  into  the  fissura  suprasylvia,  but  if 
the  student  takes  the  trouble  to  open  the  fissure  he  will  see 
that  this  condition  is  only  apparently  so.  At  this  point 
there  is  a  more  or  less  well  developed  gyrus  hidden  from 
view. 

The  facies  dorsalis  of  the  lobus  parietalis  is  divided,  in 
the  adult  specimen,  by  three  well  developed  sulci,  that  may 
be  named,  sulcus  lateralis,  sulcus  medialis  and  sulcus  inter- 
media, which  run  in  a  caudo-laterad  direction,  parallel  with 
the  caudal  portion  of  the  fissura  suprasylvia. 

These  sulci  divide  the  lobi  into  four  gyri,  an  external,  an 
internal  and  two  mesial.  These  gyri  become  larger  and 
longer  from  the  fissura  longitudinalis,  laterad.  They  run 
to  the  polus  posticus,  and  at  irregular  intervals  are  divided 
by  transverse  depressions  that  form  shallow  sulci.  These 
four  parietal  gyri  are  very  constant,  and  in  no  instance  was 
there  observed  any  evidence  of  the  separation  of  a  lobus  oc- 
cipitalis. The  gyrus  lateralis,  in  many  instances,  extends 
cephalad  to  the  fissura  cruciata,  and,  winding  around  the 
extremity  of  this  fissure,  forms  a  connection  with  the  lobus 
frontalis.  This  arrangement  is  nicely  shown  in  the  right 
hemisphere  as  seen  in  Plate  V. 

In  most  cases  the  fissura  cruciata  lies  beneath  the  os  pari- 
etale,  but  occasionally  it  lies  directly  beneath  the  sutura 
eoronalis,  and  thus  the  parietal  lobe  is  alm.ost  wholly  cov- 
ered by  the  parietal  bone. 

Slight  variations  in  the  manner  of  the  arrangement  of 
some  of  the  gyri  and  sulci  are  seen  in  most  specimens.  In 
fact,  the  arrangement  is  not  always  the  same,  even  in  the 
two  hemispheres  of  the  same  brain.  The  gyri  and  sulci 
of  the  human  enaphalon  are  not  exempt  from  such  varia- 
tions. The  fissura  cerebri  lateralis  (Sylvius),  however, 
never  varies ;  it  is  invariably  in  the  same  relative  position. 

Professors    Simpson   and   King  of   Cornell   University* 


♦Quarterly  Journal  of  Experimental  Physiology,  Vol.  IV,  No.  1, 
1911. 


ANATOMY   OP    THE   BRAIN 


35 


have  done  a  splendid  piece  of  research  on  the  motor  areas 
of  the  cerebrum  of  the  sheep,  which  must  be  mentioned  in 
this  connection  and  which  we  have  illustrated  by  three 
figures :  A.  B.  C.  taken  from  plates  V,  VIII  and  IX. 
These  phj'siologists  place  these  centres  in  the  laryrus  fron- 


FIG.  A. 

'riii.s  fiirure  illnstrates  the  dorsal  surface  of  the  l)rain.  The 
lines  and  dots  on  the  super  fi-ontal  convolntion  of  the 
left  cerebral  hemisphere  show  the  motor  areas. 


talis  superior  of  the  left  hemispherium.  They  occupy  the 
exposed  surface  of  the  gyrus  to  within  a  short  distance 
of  its  vt'ntral  border.     Tliis  excitable  area  winds  over  the 


36 


ANATOMY   OF   THE   BRAIN 


free  border  of  the   gyrus  onto   its  mesial  surface  for  a 
distance  of  1  mm. 

They  have  not  only  shown  where  the  motor  area  is  lo- 


FIG.  B. 

Frontal  elevation  of  the  cerebrum  showing*  the  motor  areas 
and  their  relations  to  each  other. 


FIG.    C. 

Showing  the  mesial  surface  of  the  left  cerebral  hemisphere 
with  motor  areas. 


ANATOMY   OP    THE   BRAIN  37 

Gated,  but  they  have  worked  out  the  location  of  the  specific 
centres  of  the  various  groups  of  muscles. 

These  figures  show  the  positions  of  the  four  different 
centres  numbered  1,  2,  3  and  4. 

1.  Muscles  of  the  face,  mouth  and  tongue. 

2.  Muscles  of  the  head  and  eye. 

3.  Muscles  of  the  fore  limbs. 

4.  Muscles  of  the  hind  limbs. 

Their  locations  should  be  marked  in  on  the  drawings 
that  are  made  of  the  cerebral  gyri  and  sulci,  not  for- 
getting the  area  involved  on  the  facies  medialis  cerebri. 


38  ANATOMY   OF   THE   BRAIN 


CHAPTER  IX. 

DORSAL  SURFACE   OF  THE  CEREBELLUM. 

As  the  heraisphaeria  cerebri  diverge  (Plate  V)  by  the 
opening  of  the  caudal  extremity  of  the  fissura  longitudinalis 
cerebri,  we  see  the  cephalic  elevation  of  the  fades  cerebelli 
dorsalis. 

In  the  centre  will  be  seen  a  large  and  more  or  less  inter- 
rupted ridge  called  the  vermis  cerebelli  with  its  surface 
marked  by  numerous  transverse  sulci  situated  quite  close 
together  and  separating  the  narrow  folia  cerebelli. 

The  vermis  cerebelli,  as  viewed  from  the  dorsal  aspect, 
appears  to  run  in  a  caudal  direction,  reaching  a  plane  al- 
most as  high  as  the  faeies  cerebri  dorsalis;  it  then  turns 
suddenly  ventrad  to  reach  the  dorsal  surface  of  the  medulla 
oblongata,  where  it  turns  again  and  takes  a  cephalic  direc- 
tion, where  the  convexities  of  the  folia  lie  against  the  dorsal 
surface  of  the  medulla  oblongata. 

These  folia  are  very  flat  portions  of  the  cerebellar  sub- 
stance, and  are  composed,  like  other  parts  of'  the  brain, 
of  substantia  grisea  and  substantia  alba.  The  former  lies 
on  the  two  surfaces  and  the  convexity  of  each  folium. 
Deep  fissures  extend  down  between  the  several  folia  carry- 
ing the  substantia  grisea  with  them  to  the  bottom.  When 
these  folia  are  cut  transversely,  as  in  the  sagittal  section 
of  the  vermis,  a  very  beautiful  tree-like  arrangement  of 
grey  and  white  matter  is  seen,  called  the  arbor  vitae,  as 
shown  in  Plate  VIII,  and  described  in  this  and  in  Chapter 
XIII.  The  large  thick  limbs  can  be  seen  diverging  from 
the  central  white  substance,  the  corpus  medullare  cerebelli ; 
and  from  these  limbs  smaller  branches  spring  like  the 
branching  of  a  tree. 

If  the  cerebellum  be  detached  from  the  rest  of  the  en- 
cephalon  the  cephalic  portion  of  the  vermis  will  also  turn 
ventrad  and  then  eaudad;  the  apices  of  the  vermis  thus 
come  close  together,  and  in  many  specimens  touch,  as  they 
lie  suspended  in  the  cavity  of  the  ventriculus  quartus. 


ANATOMY    OF    THE   BRAIN  39 

The  vermis  can  be  divided  into  five  lobes  by  four  fissures. 
According  to  Bradley*  the  fissures  enumerated  in  a  cephalo- 
caudad  direction  may  be  called,  fissure  I,  fissure  II,  fissure 
III  and  fissure  IV,  and  the  lobes  A,  B,  C,  D  and  E  (Plate 
VIII). 

In  the  ventral  part  of  the  concavity  on  the  cephalic  sur- 
face of  the  vermis  will  be  seen  a  distinct  horizontal  fissure 
called  fissure  I,  Plate  VIII.  That  portion  of  the  ver- 
mis vertral  to  this  fissure  is  lobe  A ;  the  major  part  of 
which  is  characterized  by  such  short  folia  that  it  may  be 
called  the  vermis  cerebelli  minor;  furthermore,  this  par- 
ticular part  is  separated  from  the  remainder  of  lobe  A 
by  quite  a  distinct  fissure.  Near  the  centre  of  the  oblique 
cephalic  surface  will  be  observed  a  well  marked  and  sharply 
curved  fissure  with  its  convexity  directed  dorsad;  this  is 
fissure  II. 

Lobe  B  lies  between  fissures  I  and  II.  About  5  cm.  from 
the  dorsal  extremity  of  the  caudal  surface  is  fissure  III. 

Lobe  C  occupies  the  space  between  fis.sures  II  and  III. 
On  the  ventral  surface  of  the  remaining  portion  of  the 
vermis  is  fissure  IV,  separating  lobes  D,  and  E  (Plate 
VIII). 

A  section  of  the  vermis  cerebelli  minor  is  ver^-  clearly 
shown  in  Plate  XXX,  in  Fig.  3.  The  caudal  extremity  of 
this  portion  of  the  vermis  can  be  seen  by  depressing  the 
medulla  oblongata. 

On  either  side  of  the  vermis  are  the  hemisphaeria  cere- 
belli; on  an  ordinary  inspection  the  facies  cerebelli  lateralis 
(Plate  VI)  might  be  said  to  j) resent  for  examination  three 
well  marked  lobes  separated  by  two  fissures.  These  lobes, 
in  a  general  way,  follow  the  same  general  arcuate  course 
as  the  vermis,  arching  dorso-caudad  and  then  ventrad,  and 
may  be  named,  iobus  superior,  lobus  medial  is,  and  lobus 
inferior.  This  simple  arrangement,  however,  will  be  found 
greatly  modified  on  a  closer  inspection  and  no  small  degree 


*0n  the  development  and  homology  of  the  mammalian  cerebellar 
tissues.  By  O.  Charnock  Bradley,  M.  B.,  Professor  of  Anatomy, 
Royal  Veterinary  College,  I'^dinburgh.  Journal  of  Anatomy  and 
Physiology  Vol.  XXXVII,   1903. 


40  ANATOMY   OF   THE   BRAIN 

of  complexity  exists,  particularly  in  the  ventral  portion 
of  the  hemisphere. 

At  the  extreme  ventral  part  of  each  hemisphere  is 
a  small  lobule  made  up  of  six  or  seven  folia,  called  the  floc- 
culus (Plate  VI).  Between  the  flocculus  and  the  lobus  su- 
perior is  a  long  serpentine  lobe  called  the  paraflocculus. 
The  paraflocculus  is  said  to  be  separated  from  the  lobus  su- 
perior by  a  distinct  fissure,  but  there  are  many  instances  in 
the  mature  specimen  where  the  caudal  extremity  of  the  lobus 
superior  appears  to  be  continuous  with  the  paraflocculus. 
The  three  or  four  cephalic  folia  of  the  iobi  superiores  are  in 
direct  continuity  across  the  vermis. 

m 


ANATOMY   OF   THE   BRAIN  4:1 


CHAPTER  X. 


LATERAL  SURFACE  OF  THE  CEREBRUM. 
The  fades  lateralis  cerebri  (Plate  VI)  of  the  hemisphae- 
rium  cerebri  does  not  present  the  same  regularity  in  the  ar- 
rangement of  its  gyri  and  sulci,  as  is  found  on  the  facies 
dorsalis.  In  fact  there  are  only  two,  the  fissura  cerebri 
lateralis  (Sylvii),  and  the  fissura  rhinalis  (fissura  limbica 
of  Turner),  that  are  constant. 

About  3.5  cm.  caudad  to  the  polus  frontalis  will  be  seen 
the  fissura  cerebri  lateralis  beginning  on  the  facies  dorsalis 
about  2  cm.  laterad  to  the  fissura  longitudinalis,  and,  run- 
ning directly  ventrad  for  about  2  cm.,  divides  into  a  ramus 
posterior  and  ramus  anterior;  the  former  runs  caudad  only 
a  short  distance  and,  turning  sharply  ventrad,  ends  in  the 
fissura  rhinalis  where  the  tractus  olfactorius  unites  with  the 
lobus  hippocampi.  The  ramus  anterior  is  in  most  instances 
carried  cephalad  in  a  zig-zag  manner,  somewhat  parallel 
with  the  external  border  of  the  tractus  olfactorius. 

The  fissura  rhinalis  separates  the  tractus  olfactorius  and 
the  lobus  hippocampi  from  the  cerebrum,  and  forms  the 
dividing  line  between  the  facies  lateralis  cerebri,  and  the 
facies  ventralis  cerebri. 

The  cephalic  extremity  of  this  fissure  ends  in  the  sulcus 
olfactorius,  not  shown  in  Plate  VI;  the  caudal  termination 
is  on  the  mesial  surface  of  the  cerebrum  near  the  polus 

posticus.  . 

Between  the  diverging  rami  of  the  fissura  lateralis  cerebri 
and  the  fissura  rhinalis  is  a  very  constant  lobe,  called  the 
lobus  centralis  (the  insula,  or  the  island  of  Reil).  This 
lobus  centralis  at  its  caudal  extremity  very  frequently  pre- 
sents three  well-marked  small  convolutions,  the  central  one 
of  which  rests  in  the  antrle  formed  by  the  diverging  rami  of 
the  fissura  lateralis  cerebri.  These  convolutions  extend  into 
the  substance  of  the  hemisphere  and  can  be  easily  shown  by 
slightly  elevating  the  ventral  extremities  of  the  gyrus  syl- 
viacus.     In  fact,  the  lo})US  centralis  may  be  so  depressed 


42  ANATOMY    OF    THE    BRAIN 

that  the  ventral  extremities  of  the  gyrus  sylviacus  appear  to 
hang  over  it,  suggesting  its  partial  occlusion ;  it  is  only  in 
the  older  specimens  that  this  overlapping  is  so  well  marked. 
In  all  cases,  however,  the  rami  of  the  fissura  lateralis 
cerebri  dip  well  in  toward  the  centre  of  the  hemisphaerium, 
thus  cutting  off  the  insula  as  a  separate  lobe. 

The  lower  projecting  ends  of  the  gyrus  sylviacus  suggest 
very  strongly  the  operculum  in  man;  the  ventral  extremi- 
ties of  this  gyrus  might  well  be  called  the  operculum, 
in  the  sheep. 

There  will  be  seen  in  almost  all  encephala  a  large  gyrus 
that  has  been  mentioned  several  times  already;  this  is  the 
gyrus  sylviacus  (arcuatus).  This  gyrus  arches  over  the 
dorsal  extremity  of  the  fissura  lateralis  cerebri.  There  is  in 
many  cases  a  well-marked  gyrus  lying  parallel  with  and 
dorsal  to  the  tractus  olfactorius,  the  gyrus  orbit alis;  this 
gyrus  is  in  some  cases  quite  distinctly  separated  from  the 
lobus  centralis.  Just  dorsad  to  the  cephalic  ramus  of  the 
fissura  lateralis,  lies  the  gyrus  frontalis  inferior;  these  two 
gyri,  are,  however,  generally  broken  up  into  a  number  of 
small  irregular  convolutions.  • 

The  arrangement  of  the  sulci  and  gyri  on  the  faeies  later- 
alis of  the  lobus  temporalis  follow  no  definite  order  that 
could  be  ascertained  from  a  careful  study  and  comparison 
of  the  limited  number  of  encephala  examined,  and  will  not 
be  further  discussed  at  the  present. 


ANATOMY   OP    THE   BRAIN 


43 


CHAPTER  XI. 

VENTRAL  SURFACE  OF  THE  CEREBRUM. 

The  fades  ventralis  cerebri  (Plate  VII)  of  the  encephalon 
exhibits  a  large  number  of  very  important  structures. 
That  part  of  the  cerebrum  lying:  between  the  two  sulci 
rhinales  should  be  considered  as  the  ventral  surface  of  the 
encephalon. 

At  the  cephalic  extremity  will  be  seen  two  large  oval 
masses  of  matter  placed  obliquely;  these  are  the  hulhi  olfac- 
torii,  very  large  in  macrosmatic  animals.  These  bulbs  lie 
in  the  deep  sulci  olfactorii;  their  cephalic  extremities  turn 
slightly  dorsad  in  front  of  the  lobi  frontales.  Each  bulbus 
olfactorius  is  attached  to  the  cerebrum  by  three  radices. 

The  radix  medial  is  passes  caudad  and  mediad  to  the  facies 
medialis  and  unites  with  the  subcallosal  extremity  of  the 
gyrus  cinguli;  it  is  composed  of  substantia  grisea,  and  is 
always  well  marked. 

The  radix  lateralis  passes  laterad  and  caudad  to  unite 
with  the  cephalic  extremity  of  the  lobus  hippocampi  at  its 
outer  part;  the  lateral  margin  of  the  radix  lateralis  is  di- 
rectly continuous  with  the  external  border  of  the  lobus  hip- 
pocampi. These  borders  form  the  internal  or  ventral  lip 
of  the  fissura  rhinalis. 

The  radix  lateralis  is  always  well  marked  and  much 
larger  than  the  radix  medialis;  it  consists  of  an  external 
larger  portion  of  substantia  grisea,  and  an  internal  part  of 
substantia  alba  much  less  in  quantity  than  the  substantia 

grisea. 

The  radix  intermedia  is  composed  entirely  of  substantia 
alba,  derived  principally  from  the  commissura  anterior,  to 
be  subsequently  traced  and  described.  This  so-called  radix 
does  not  appear  on  the  surface  of  the  encephalon  but,  on 
slightly  elevating  the  bulbus  olfactorius,  or  by  dissecting 
away  the  substantia  grisea  which  constitutes  the  locus  per- 
foratus  anterior,  as  described  in  a  later  dissection  the  cor- 
responding extremity  of  the  commissura  or  radix  is  plainly 
.seen   f  Plate  XIX). 


44  ANATOMY   OP   THE   BRAIN 

Between  the  sulcus  olfactorius  and  the  fissura  longitudi- 
nalis  cerebri  is  seen  the  gyrus  rectus,  which  winds  around 
the  cephalic  extremity  of  the  sulcus  olfactorius  and  then 
takes  a  course  directly  eaudad,  parallel  with  the  gyrus  orbi- 
talis. 

The  large  triangular  or  quadrilateral  space  (espace  quad- 
rilatiere  of  Broca)  formed  by  the  diverging  radices  olfac- 
toriae,  is  called  the  locus  perforatus  anterior.  It  consists  of 
substantia  grisea  marked  by  a  large  number  of  perforations, 
through  which  pass  the  antro-mesial  and  the  antro-lateral 
arteries  arising  from  the  A.  cerebri  anterior  and  the  A. 
cerebri  media  respectively  to  be  distributed  to  the  corpus 
striatum. 

After  a  specimen  has  been  taken  from  formalin  and 
placed  in  water  for  twenty-four  hours,  examine  the  ventral 
surface  just  cephalad  to  the  tractus  opticus.  In  this  re- 
gion, a  small  band  of  substantia  grisea  may  be  seen  ex- 
tending from  the  mesial  border  of  the  lobus  hippocampi 
near  its  cephalic  extremity,  to,  and  bending  around  onto 
the  facies  medialis  cerebri.  Here  it  blends  with  the  sub- 
callosal extremity  of  the  gyrus  cinguli. 

Just  eaudad  to  the  loci  perforati  anteriores  is  seen  a 
crucial  arrangement  of  substantia  alba,  the  chiasma  opti- 
cum. 

Passing  cephalad  from  the  lateral  extremities  of  the 
chiasma  opticum  (optic  commissure)  are  two  large  nerves 
the  nervi  optici  that  have  been  cut  in  removing  the 
encephalon. 

Passing  latero-caudad  from  the  chiasma,  are  two  large 
bands  of  substantia  alba  called  the  tracti  optici;  these  tracts 
soon  disappear  dorsad  to  the  lobi  hippocampi,  and  will  be 
traced  to  their  destination  in  a  subsequent  dissection. 

Immediately  behind  the  chiasma  opticum  is  a  projection 
of  substantia  grisea,  the  infundihulum,  which  connects  with 
the  hypophysis  (pituitary  body,  not  shown  in  Plate  VII, 
but  drawn  in  Plate  XIX) ,  The  hypophysis  can  be  liberated 
from  the  fossa  hypophyseos  (sella  turcica),  when  freeing 
the  encephalon  from  the  basis  cranii  interna,  by  making  an 
incision  through  the  dura  at  its  attachments  to  the  margins 


ANATOMY    OF    THE   BRAIN 


45 


ol:  the  fossa,  then,  by  gently  rupturing  the  bands  of  connect- 
ive tissue  that  attach  the  hj'pophysis  to  the  fossa,  it  can  be 
removed  without  injury. 

In  the  centre  of  the  infundibulum  is  a  large  opening  lead- 
ing into  the  ventriculus  tertius.  The  infundibulum  appears 
to  rest  upon  a  triangular  eminence  of  substantia  grisea,  the 
tiiher  cinereum,  in  the  inverted  specimen. 

The  caudal  extremity  of  the  tuber  cinereimi  presents  in 
most  cases  an  eminence  more  or  less  bilobed,  called  the 
corpora  mamillaria  (corpora  albicantia,  bulbi  fornicis).  In 
some  instances  there  is  apparently  but  one  corpus  mamil- 
lare,  as  superficially,  in  these  cases,  there  is  only  one  emi- 
nence. 

About  two  per  cent  of  all  the  specimens  studied  show  a 
distinct  bilobed  corpora  mamillaria;  quite  as  marked  as 
that  which  obtains  in  the  human  brain,  and  in  those  of  the 
primates.  In  class  work,  when  a  specimen  of  well-defined 
bilobed  mamillary  body  is  found,  it  should  be  shown  to 
each  student  and  then  preserved  in  the  neurological 
laboratory  for  demonstration  purposes. 

In  the  median  line  caudad  to  the  corpora  mamillaria  is 
a  very  marked  depression,  the  fossa  inter  peduncular  is 
(locus  perforatus  posterior,  pons  Tarini),  at  the  bottom  of 
which  is  the  substantia  perforata  posterior.  The  fossa  is 
bounded  on  each  side  by  large  masses  of  white  matter,  the 
pedunculi  cerebri  (crura  cerebri)  composed  of  fibres  which 
convey  impulses  to  and  from  the  cerebrum. 

Rising  from  the  ventral  surface  of  the  pedunculi  cerebri 
and  close  to  their  internal  border  will  be  seen  the  N7i.  oculo- 
motorii  (third  pair  of  cerebral  nerves).  Winding  cephalad 
from  the  dorsal  surfaces  of  the  pedunculi  will  be  seen  two 
nerves,  much  smaller  than  the  Nn.  oculomotorii ;  these  are 
the  Nn.  Irochleares  (pathetici,  fourth  pair  of  nervi  eere- 
brales).  Lying  between  the  pedunculi  cerebri,  close  to  the 
cephalic  border  of  the  pons,  is  a  small  quantity  of  grey 
matter,  very  marked  in  some  cases;  this  is  the  nucleus 
interpeduncularis. 

Tracing  the  pedunculi  cerebri  caudad  they  appear  to  pass 
under  a  thick  transverse  band  of  tissue,  the  pons  (Varolii)  ; 


4'6  ANATOMY   OP    THE   BRAIN 

and  at  each  extremity  of  the  pons  is  a  very  large  nerve,  the 
N.  trigeminus  (fifth  pair,  trifacial). 

Caudad  to  the  pons  is  another,  but  somewhat  indistinct 
transverse  band  of  fibres,  the  trapezium,  which  in  some  en- 
cephala  is  scarcely  perceptible,  while  in  others  it  is  very 
readily  identified. 

Arising  from  the  ventral  surface  of  the  trapezium  near 
the  middle  lino  are  the  Nn.  ahducentes  (sixth  pair)  about 
the  size  of  the  Nn.  trochleares. 

Coming  apparently  from  the  lateral  aspect  of  the  tra- 
pezium are  two  nerves,  about  the  size  of  the  oculomotorii ; 
the  cephalic  nerve  is  the  N.  facialis  (seventh  pair,  portia 
dura)  ;  the  caudal  nerve  is  the  N.  acusticus  (eighth  pair, 
portio  mollis). 


ANATOMY   OP   THE   BRAIN  47 


CHAPTER  XII. 

THE  MEDULLA   OBLONGATA. 

The  medulla  oblongata  forms  the  large  club-like  body 
directly  caudad  to  the  trapezium ;  it  gradually  decreases  in 
size  until  it  reaches  the  neighborhood  of  the  medulla  spin- 
alis, at  the  level  of  the  first  cervical  nerve.  At  this  point 
the  decrease!  in  size  is  very  abrupt,  until  it  attains  the 
dimensions  of  the  latter  structure.  The  central  nervous 
system  is  prolonged  caudad  as  the  medulla  spinalis,  a  long 
cylindrical  mass  of  nervous  matter  which  gives  off  the  nervi 
spinal  es. 

From  the  sides  of  the  medulla  oblongata,  beginning  just 
caudad  to  the  trapezium  there  spring  the  roots  of  three 
large  nerves,  N.  glossopharyngeus  (ninth  pair),  N.  vagus 
(tenth  pair,  par  vagum,  pneumogastric)  and  the  N.  acces- 
sorius  (eleventh  pair,  spinal  accessory).  From  the  ventral 
surface  of  the  medulla  oblongata  about  5  mm.  from  the 
midline,  there  arise  eight  of  ten  roots,  which  unite  to  form 
the  N.  Jiypoglossus  (twelfth  pair). 

If  the  instructions  to  cut  the  nervi  cerebrales  close  to 
their  foramina  of  exit  have  been  followed,  there  will  be  no 
difficulty  in  identifying  the  twelve  pairs  of  cranial  nerves 
just  enumerated. 

The  encephalon  should  now  be  placed  under  water  and 
the  ventral  surface  carefully  cleaned,  removing  all  vessels 
and  the  trabeculae  subarachnoideales. 

Care  must  be  taken  NOT  to  remove  the  pia  mater  in 
making  this  dissection,  for  in  so  doing  the  attachments  of 
the  filaments,  as  they  emerge  to  form  the  nervi  cerebrales 
would  be  ruptured;  thus  very  materially  reducing  the 
value  of  the  preparation. 

One  who  has  removed  the  medulla  spinalis  for  the  first 
time  will  surely  be  impressed  with  the  apparently  num- 
berless nerve  filaments  that  attach  the  nervi  spinales  to 
the  cord,  parti(!ularly  in  the  case  of  those  that  go  to  njake 
tlie  Cauda  equina.     This  same  arrangement  obtains  on  the 


48  ANATOMY    OF   THE   BRAIN 

ventral  and  lateral  surfaces  of  the  brain  stem.  In  this 
connection,  note  the  N.  oculomotorius,  N.  glosso-pharyn- 
genus,  N.  vagus,  N.  accessorius  and  N.  hypoglossus. 

A  very  beautiful  preparation  can  be  made  if  the  work 
is  carefully  done,  particularly  so  if  the  low  power  of  a 
good  dissecting  microscope  is  brought  into  requisition. 
Make  drawings  of  the  dorsal  and  lateral  surfaces. 


ANATOMY   OF   THE   BRAIN 


CHAPTER  XIII. 


49 


MESIAL  SURFACE  OF  THE  CEREBRUM  AND 
CEREBELLUM. 

FACIES    MEDIALB3    CEREBRI. 

[See  Plate  VIII. ] 
Gently  pull  apart  the  hemispliaeria  cerebri  until  the  dor- 
sal surface  of  the  corpus  callosum  (a  large  band  of  trans- 
verse fibres  uniting  the  cerebral  hemispheres)  is  seen;  place 
the  heel  of  the  brain-knife  in  the  fissura  longitudinalis 
cerebri,  resting  the  edge  of  the  knife  on  the  corpus  callo- 
sum. AVith  one  sweep  of  the  Imife,  cut  the  encephalou 
completely  through  and  the  facies  medialis  cerebri  is  ex- 
posed. 

This  surface  is  of  special  interest  to  the  medical  student 
as  its  general  appearance  and  construction  more  closely 
resembles  that  of  the  corresponding  area  of  the  human 
encephalon  than  any  other  of  the  regions  that  have  been 
studied. 

The  corpus  callosum  is  the  elongated  mass  of  white  mat- 
ter lying  about  the  centre  of  the  exposed  surface  and  pass- 
ing cephalo-ventrad.  The  cephalic  extremity,  the  genu 
corporis  callosi  (knee),  approaches  to  within  about  2  cm. 
of  the  polus  frontalis,  then  bending  ventrad  and  caudad 
ends  in  the  rostrum  corporis  callosi.  The  caudal  extremity 
ends  in  a  blunt  club-like  enlai-gement,  called  the  splenium 
corporis   callosi. 

The  mesial  surface  of  the  cerebrum  very  largely  sur- 
rounds the  corpus  callosum  as  the  central  structure,  and, 
like  the  other  surfaces  of  the  cerebrum,  is  for  the  most 
part  subdivided  by  a  number  of  fissures  into  gyri.  The 
selection  of  the  proper  names  for  the  various  fissures  and 
gyri  expased  to  view  on  this  surface,  caused  considerable 
anxiety;  and  if  proper  I'espect  has  not  been  paid  to  the 
homologies,  the  censure  must  be  laid  to  a  perhaps  excessive 
desire  to  pave  the  way  for  the  student  in  medicine  to  grasp 


50  ANATOIMY    OF    THE   BRAIN 

the  complex  arrangement  obtaining  on  the  mesial  surface 
of  the  encephalon  of  man.  The  various  names  have  been 
selected  that  appear  to  describe  in  the  clearest  and  shortest 
manner  the  conditions  found  on  the  part  under  considera- 
tion, and  little  regard  has  been  paid  to  their  significance 
from  the  standpoint  of  comparative  anatomy,  with  the  ex- 
ception of  some  few  terms  selected  from  the  anatomy  of 
the  human  brain. 

The  well  marked  gyrus  lying  immediately  dorsad  to 
the  corpus  callosum  is  the  gyrus  cinguli.  This  gyrus  ex- 
tends through  the  entire  length  of  the  corpus  callosum,  Avith 
its  cephalic  extremity  turning  sharply  around  the  genu 
corporis  callosi,  and  proceeding  caudad,  follows  the  course 
of  the  rostrum  corporis  callosi,  and  ending  on  the  facies 
medialis  cerebri  near  its  ventral  border. 

Frequently  the  radix  medialis  bulbi  olfactorii  can  be 
very  distinctly  seen  passing  to  the  cephalic  extremity  of 
this  gyrus.  The  caudal  extremity  of  the  gyrus  cinguli 
passes  around  the  splenium  corporis  callosi  and  unites 
with  the  caudal  extremity  of  the  lobus  hippocampi.. 

The  sulcus  corporis  callosi  lies  between  the  gyrus  cinguli 
and  the  corpus  callosum. 

Dorsal  to  the  gyrus  cinguli  there  is  seen  a  large  gyrus 
intermedins,  marked  off  from  the  gyrus  cinguli  by  the 
sulcus  cinguli.  Occasionally  this  sulcus  is  poorly  de- 
veloped or  it  may  be  absent  dorsal  to  the  caudad  third 
of  the  corpus  callosum,  and  then  the  gyrus  cinguli  and 
the  gyrus  intermedins  appear  to  fuse  and  form  one  very 
large  convolution  which  occupies  the  major  portion  of 
the  facies  medialis,  constituting  the  gyrus  fornicatus  of 
comparative  anatomists. 

That  portion  of  the  gyrus  intermedia  lying  dorsad  to 
the  central  third  of  the  corpus  callosum  is  usually  very 
wide  and  in  the  majority  of  instances  reaches  to  the  dorsal 
margin  of  the  facies  medialis  cerebri. 

The  gyrus  marginalis  posterior  is  separated  from  the 
caudal  half  of  the  gyrus  intermedins  by  the  sulcus  sple- 
nialis  (fissura  limbiea  of  Broca)  ;  this  fissure  is  very  con- 
stant in  all  mammals,  even  occurring  in  the  Lissencephala 


ANATOMY   OF    THE   BRAIN  51 

(smooth-brained).  It  can  be  traced,  in  abnost  all  speci- 
mens, to  the  dorsal  surface  of  the  gyrus  frontalis  superior 
as  a  small  fissure  or  notch,  about  4  mm.  cephalad  to  the 
fissura  cruciata ;  Figs,  a,  b,  and  c  and  plate  IX.  The  gyrus 
passes  well  cephalad  in  the  sheep's  brain  and  ends  about 
the  centre  of  the  dorsal  margin  of  the  facies  medialis. 

The  sulcus  parolfaclorius  lies  between  the  cephalic  por- 
tion of  the  gyrus  intermedins  and  the  corresponding 
margin  of  the  facies  medialis,  marking  off  the  gyrus  mar- 
giiialis  anterior.  In  a  number  of  instances  the  sulcus 
parolfaetorius  is  not  well  developed,  but  is  broken  up  into 
numerous  straight  sulci,  having  a  tangentical  relation  to 
the  sulcus  cinguli. 

The  sulcus  splenialis,  the  sulcus  cinguli,  the  sulcus  cor- 
poris callosi  and  the  fissura  rhinalis  end  on  the  tentorial 
surface  of  the  hemisphere. 

The  facies  medialis  cerebelli  can  be  nicely  seen  while 
studying  the  corresponding  surface  of  the  cerebrum,  show- 
ing the  lobes  of  the  vermis  cerebelli  as  indicated  in  Plate 
VIII  by  the  letters  a,  h,  c,  d,  e.  This  lissection  also  shows 
the  cut  surfaces  of  those  structures  that  lie  ventral  to  the 
pallium. 

As  before  noted,  the  radix  medialis  bulbi  olfactorii  can 
be  seen  approaching  the  gyrus  cinguli.  About  1  cm.  caudad 
to  the  tip  of  the  rostrum  corporis  callosi  and  a  little 
ventrad,  is  the  commissura  anterior  composed  of  substantia 
alba,  cut  across.  This  commissure  is  easily  identified,  and 
can  be  traced  to  the  corresponding  bulbus  olfactorius  if 
desired,  as  shown  in  Plate  XIX.  The  dissection  of  the  en- 
tire commissure  will  be  described  in  a  later  part  of  the 
work. 

Caudad  to  the  eomiiiissure  is  the  pars  tecta  columnae 
fornicis,  the  dissection  of  which  will  be  described  later. 

This  will  be  a  convenient  place  to  describe  the  cephalic 
and  ventral  walls  of  the  ventriculus  tertius,  as  formed  by 
the  lamina  terininalis  and  the  tuber  cinereum.  If  the 
facies  medialis  cerebri  be  carefully  examined,  an  indistinct 
layer  of  tis.sue  can  be  demonstrated,  extending  caudad  in 
a    zig-zag    manner    from    the    terminal    extremity    of    the 


52 


ANATOMY    OF    THE   BRAIN 


rostum  corporis  eallosi  to  the  comissura  anterior.  This 
layer  of  tissue  is  called  the  lamina  rostralis,  and  is  semi- 
diagramatically  shown  in  Fig.  D.  It  is  difficult  to  demon- 
strate in  most  specimens. 


FIG.  D. 

A.  The  arrow  passing  through  the  foramen  interven- 
triculare  (Monroe)  accompanying  the  plexus  chorioideus 
ventrieulari  lateralis. 

B.  Lamina  rostralis. 

C.  Lamina  terminalis. 

D.  Chiasma  opticum. 

E.  Tuber  cinereum. 

F.  Recessus  infundibuli. 

G.  Arrow  pointing  to  the  aperatura  mediana  ventric- 
uli  quarti  (Magendie). 

H.     Arachnoidea. 


As  the  lamina  rostralis  reaches  the  cephalic  border  of 
the  commissura  anterior,  it  blends  with  the  dorsal  portion 
of  the  lamina  terminalis  {lamina  cinerea),  a  structure  of 
considerable  importance.  The  lamina  terminalis  is  carried 
almost  perpendicularly  ventrad  to  the  region  of  the 
chiasma  opticum,  passing  some  little  distance  cephalad  to 
the  chiasma.    It  is  then  reflected  backward,  attached  closely 


ANATOMY   OF    THE   BRAIN  53 

to  the  ventral  and  caudal  surfaces  of  the  chiasma,  forming 
a  little  cavity  or  diverticulum  called  the  recessus  opticus 
ventriculi  tertii. 

After  the  lamina  leaves  the  chiasma  it  is  continued 
caudo-ventrad  as  the  tuber  cinerea  to  reach  the  corpus 
maraillare.  The  tuber  cinerea  dips  ventrad,  carrying  with 
it  a  diverticulum  from  the  ventriculus  tertius  called  the 
recessus  infundibuli,  to  reach  the  hypophysis  as  it  lies  in 
the  fossa  hypophyseos.  The  portion  of  nerve  tissue  that 
passes  ventrad  to  reach  the  hypophysis  is  the  infundib- 
ulum;  it,  together  with  the  tuber  forms  part  of  the  floor 
of  the  ventriculus  tertius. 

Ventral  to  the  splenium  corporis  callosi  rests  the  caudal 
extremity  of  the  fornix  and  beneath  this,  the  fasciola  cin- 
erea; beneath  the  fasciola  is  the  central  portion  of  the  fis- 
sura  transversa  cerebri,  containing  the  pia  and  the  V. 
magna  cerebri. 

Just  ventrad  to  the  fissura  transversa  cerebri  are  two 
small  structures,  the  trigona  hahenulae  and  caudad  to  this 
the  corpus  pineale ;  ventrad  from  this  latter  structure  is 
the  lamina  pineale. 

Directly  caudad  to  the  corpus  pineale  are  two  pairs  of 
bodies  of  unequal  size,  the  corpora  quadrigemina,  resting 
on  the  lamina  quadrigemina,  cephalad  to  which  is  seen  very 
indistinctly  the  commissura  posterior. 

Ventral  to  the  lamina  is  a  canal  leading  from  the  ven- 
triculus tertius  to  the  ventriculus  quartns;  this  is  the 
aquaeductus  cerebri  (aqueduct  of  Sylvius,  iter  a  tertio  ad 
quartum  ventriculum). 

Filling  in  the  space  which  separates  the  commissura  an- 
terior from  the  commissura  posterior  is  a  large  round  sur- 
face of  substantia  grisea,  the  mesial  surface  of  the  thalamus 
opticus  of  the  corresponding  hemisphere.  This  structure 
forms  a  considerable  portion  of  the  lateral  wall  of  the 
ventriculus  tertius.  A  small  quantity  of  the  substantia 
grisea  of  one  thalamus  stretches  across  the  cavity  of  the 
ventriculus  tertiu.s  and  is  attached  to  a  corresponding  por- 
tion of  the  opposite  thalamus  forming  the  massa  intermedia 


54  ANxVTOMY    OF   THE   BRAIN 

(commissura  medialis)  ;  the  cut  surface  of  the  massa  is 
almost  circular  in  outline  and  about  1  cm.  in  diameter. 

Posterior  to  the  corpora  quadrigemina  and  the  pallium 
is  seen  the  cut  surface  of  the  vermis  cerebelli  showing  the 
arrangement  of  the  substantia  alba  and  the  substantia 
grisea  called  the,  arhor  vitae.  The  central  portion,  con- 
sisting of  substantia  alba,  has  been  named  the  corpus 
medullare  cerebelli. 

Connecting  the  corpora  quadrigemina  with  the  corpus 
medullare  cerebelli  is  a  delicate  layer  of  tissue,  the  velum 
medullare  anterior  (tegmentum  ventriculi  quarti,  superior 
medullary  velum,  valve  of  Vieussens). 

The  ventricidus  quartus  is  a  large  space  lying  ventrad 
to  the  velum  medullare  anterior  and  the  cerebellum. 

Leading  from  the  caudal  extremity  of  the  ventricle  will 
be  seen  a  small  opening  the  canalis  centralis  of  the  medulla 
spinalis ;  this  canal  is  sometimes  called  the  ventriculus  me- 
dullae  spinalis,  and  it  extends  throughout  the  entire  length 
of  the  cord. 

Lying  ventrad  to  the  ventriculus  quartus  are  the  follow- 
ing structures  cut  sagittally,  in  order  cephalo-caudad ;  cau- 
dalic  extremity  of  the  pendunculus  cerebri,  together  with 
the  pons,  and  the  medulla  oblongata. 

The  structures  enumerated  as  pertaining  to  the  facies 
medialis  cerebri  must  be  identified  and  a  drawing  made 
that  will  embrace  all  of  them.  A  comparison  with  the  cor- 
responding surface  of  the  human  encephalon  should  also 
be  made. 


ANATOMY   OF   THE   BRAIN 


CHAPTER  XIV. 


55 


CEREBRAL  SUBSTANCE  AND  THE  CORPUS  CAL- 

LOSTOI. 

The  internal  architecture  of  the  encephalon  of  the  sheep 
in  a  large  number  of  parts  is  surprisingly  similar  to  the 
encephalon  of  man. 

Make  an  horizontal  section  across  both  hemisphaeria 
cerebri  on  a  level  with  the  highest  point  of  the  vermis 
cerebelli.  A  very  beautiful  arrangement  of  the  substantia 
alba  and  the  substantia  grisea  is  presented  and  illustrated 
in  Plate  X. 

The  depth  to  which  some  of  the  fissures  and  sulci  sink 
into  the  substantia  hemisphaeria  cerebri  should  be  care- 
fully noted,  as  well  as  the  thickness  of  the  substantia 
grisea  which  is  quite  uniform  throughout. 

Study  the  fissura  cerebri  lateralis,  the  fissure  coronalis, 
and  the  sulcus  splenialis  which  runs  in  an  irregular  man- 
ner well  cephalad  into  the  lobus  frontalis,  almost  parallel 
with  the  fissura  longitudinalis  cerebri. 

Examine  also  the  long  band  of  substantia  alba  that  runs 
from  the  lobus  frontalis  to  the  polus  occipitalis;  this 
band  is  very  irregular  in  outline,  and  becomes  larger  as 
it  passes  caudad.  This  appearance  is  formed  by  cutting 
oft'  transversely  the  ventral  layer  of  fibres  of  the  corpus 
callosum  and  a  large  number  of  fibres  of  the  corona 
radiata.     These  two  structures  will  be  again  referred  to. 

Owing  to  these  gyri  and  sulci  the  total  quantity  of  the 
cortex  is  nuich  greater  than  that  appearing  on  the  surface. 
It  will  also  be  noticed  that  leading  into  each  gyrus  there 
is  a  band  of  substantia  alba.  This  substantia  alba  consists 
of  medullated  nerve  fibres  that  carry  impulses  to  and  from 
the  cortical  cells  which  lie  in  the  substantia  grisea. 

Take  one  of  the  portions  of  the  cerebral  substance  that 
has  been  cut  off  and  tear  through  the  exposed  substantia 
alba  toward  the  convexity  of  the  gyrus,  and  the  white  sub- 
stance will  split  in  the  direction  in  which  the  fibres  run. 


•  56  ANATOMY    OF   THE   BRAIN 

This  shows  very  plainly  how  the  nerve  fibres,  as  they  en- 
ter a  gyrus,  are  distributed  to  its  cortex. 

In  the  further  dissection  of  the  eneephalon,  frequent  use 
of  this  tearing  process  should  be  made  for  the  purpose  of 
showing  the  direction  taken,  or  the  ultimate  termination 
of  many  definite  strands  of  fibres,  where  the  scalpel  would 
imperil  the  success  of  the  dissection. 

When  a  drawing  of  the  horizontal  section  has  been 
made,  the  fissura  longitudinalis  cerebri  should  b^  gently 
opened.  At  its  cephalic  extremity,  the  fissure  will  be  seen 
to  pass  completely  through  between  the  hemisphaeria 
cerebri  to  the  ventral  surface  of  the  eneephalon;  likewise, 
at  the  caudal  extremity,  the  fissure  will  pass  completely 
through  the  cerebrum. 

In  the  central  portion,  however,  the  fissure  is  interrupted 
by  a  very  large  band  of  transverse  fibres  of  substantia 
alba,  already  mentioned,  called  the  corpus  callosum.  A 
section  of  this  structure  has  been  noticed  on  the  facies 
medialis  encephali.  The  corpus  callosum  is  the  great 
commissure  of  the  cerebrum. 

Tear  away  as  carefully  as  possible  the  gyrusi  cinguli,  ly- 
ing dorsad  to  the  corpus  callosum  and  examine  its  exposed 
surface  (Plates  VIII,  XI,  XII,  XIII).  The  transverse  di- 
rection of  its  fibres  can  be  clearly  seen  after  the  gyri  cinguli 
have  been  removed,  yet  all  the  fibres  do  not  run  trans- 
versely; for  in  the  centre  of  the  corpus  callosum,  passing 
in  a  sagittal  direction  will  be  observed  two  strands,  the 
striae  longitudinales  mediales  (nerves  of  Lancisi). 
-  Between  these  longitudinal  striations  is  a  very  distinct 
furrow  running  parallel  with  them  called  the  raphe.  Ex- 
ternal to  the  stria  longitudinalis  medialis  on  either  side, 
there  is  another  striation,  the  stria  longitudinalis  lateralis 
lying  directly  ventral  to  the  gyrus  cinguli.  This  latter 
stria  fades  out  before  reaching  the  genu  corporis  callosi, 
and  on  its  backward  extension  fuses  with  the  caudal  ex- 
tremity of  the  lobus  hippocampi.  The  stria  longitudinalis 
medialis  can  be  traced  cephalad  around  the  genu  corporis 
callosi  to  the  crura  corporis  callosi;  traced  caudad  they 
pass  over  to  the  ventral  surface  of  the  splenium  corporis 


ANATOMY    OF    THE   BRAIN  57 

callosi  and  become  continuous  with  the  fascia  dentata  by 
way  of  the  fasciol«  einerea. 

In  the  central  portion  of  the  corpus  callosmn,  its  fibres 
assume  the  transverse  direction,  but  as  they  proceed  laterad 
they  diverge  quite  acutely  and  form  what  is  called  the 
radiaUo  corporis  callosi.  Those  fibres  constituting  the 
genu,  and  many  adjacent  fibres,  bend  in  a  latero-cephalad 
direction  toward  the  polus  frontalis  forming  what  is  called 
the  forceps  anterior  or  minor,  which  together  constitute 
about  three-fifths  of  a  circle. 

The  fibres  of  the  rostrum  radiate  ventrad  and  are  di- 
rected toward  the  corresponding  border  of  the  faeies 
medialis  of  the  lobus  frontalis.  The  fibres  constituting  the 
splenium  (Plates  XI  and  XII)  take  a  curved  caudad  di- 
rection to  reach  the  polus  occipitalis,  forming  the  forceps 
posterior  or  major,  following  very  closely  the  radiating 
distribution  assumed  by  the  fibres  of  the  genu  in  the  lobus 
frontalis;  some  fibres  of  the  corpus  callosum  are  seen 
to  pass  dorsally  to  the  lateral  side  of  the  cornu  posterius 
ventriculi  lateralis,  and  then  proceed  cephalad  to  the  ex- 
tremity of  the  lobus  hippocampi  as  shown  in  Plates  XII 
and  XVI.  This  arrangement  appears  to  be  similar  on 
the  two  sides,  though  it  is  somewhat  difficult  to  follow. 
The  direction  of  these  various  bands  of  fibres  of  the  corpus 
callosum  can  be  demonstrated  by  tearing  in  the  direction 
in  which  they  run.  Trace  carefully,  and  describe  the  ar- 
rangement of  the  fibres  of  the  genu  and  the  rostrum  by 
drawings. 

The  tapetum  is  a  layer  of  tissue  forming  the  roof  of  the 
cornu  inferius  ventriculi  lateralis,  and  the  cornu  posterius 
ventriculi  lateralis  when  present.  It  is  derived  from  the 
corpus  callosum,  and  is  described  in  the  human  encephalon. 
In  the  angle  where  the  gyrus  cinguli  fuses  with  the  ven- 
tral surface  of  the  corpus  callosum,  will  be  found  a  longi- 
tudinal band  of  association  fibres,  called  the  cimjulum 
superius   (cingulum,  a  girdle). 

This  cingulum  lies  within  the  cortex,  dorsal  to  the  corpus 
callosum  and  can  be  easily  distinguished  from  the  stria 
longitudinalis  lateralis;  it  is  most  readily  found  where  the 


58  ANATOMY    OF   THE   BRAIN 

gyrus  cinguli  meets  the  corpus  callosum.  This  tract  is 
quite  narrow  where  it  rests  upon  the  (Corpus  callosum,  but 
increases  in  size  as  it  passes  cephalad  and  caudad.  Traced 
cephalad  it  spreads  out  like  an  open  fan,  and,  following 
the  fibres  of  the  genu,  is  distributed  to  the  region  of  the 
apex  of  the  lobus  frontalis.  Following  the  tract  caudad, 
it  can  be  traced  around  the  caudal  border  of  the  splenium, 
passing  ventrad,  and  then  cephalad  to  end  apparently  in 
the  substantia  alba  of  the  lobus  hippocampi. 

The  strand  should  be  dissected  out  before  completing 
the  study  of  the  fibres  of  the  splenium,  the  fibres  of  which 
tear  very  nicely  to  their  termination  in  the  cortex  of  the 
gyri  at  the  caudal  extremity  of  the  pallium. 

A  drawing  is  to  be  made  showing  the  general  shape  of 
the  corpus  callosum,  with  the  central  longitudinal  fibres ; 
the  drawing  to  likewise  show  on  one  side  the  lateral  fibres, 
and  on  the  opposite  side  the  cingulum  superius. 

Make  a  sagittal  incision  through  the  cephalic  two-thirds 
of  the  corpus  callosum  just  to  one  side  of  the  stria  longi- 
tudinalis  medialis;  the  knife  will  be  found  to  enter  a  large 
cavity,  the  ventriculus  lateralis  (Plate  XIII).  The  corpus 
callosum  will  be  seen  to  form  the  roof  of  this  portion  of 
the  ventricle.  The  genu  corporis  callosi,  and  the  rostrum 
corporis  callosi  as  they  turn  ventrad  and  caudad,  form 
respectively  the  cephalic  boundary  and  the  extreme  cephalic 
portion  of  the  floor  of  the  ventricle.  A  portion  of  this 
arrangement  is  shown  in  Plate  VIII. 

Pull  away  in  an  outward  direction  the  cut  fibres  of  the 
corpus  callosum,  and  expose  the  cavity  of  the  ventricle. 
At  the  outer  angle  of  the  ventricle,  and  attached  to  the 
ventral  surface  of  the  corpus  callosum,  is  another  band  of 
longitudinal  fibres  called  the  fasciculus  suhcallosus  (cingu- 
lum inferius). 

The  fasciculus  subcallosus  (Plates  XII  and  XVI)  is 
very  distinct  from  any  of  the  other  structures  found  in  the 
ventriculus  lateralis.  The  fibres  of  this  fasciculus,  more- 
over, are  very  closely  attached  to  the  ventral  surface  of 
the  corpus  callosum,  but  the  fibres  of  the  two  structures 
do  not  in  any  way  intermingle. 


ANATOMY    OF    THE   BRAIN  59 

The  structure  is  exposed  by  very  o^ently  elevating  the 
fibres  of  the  corpus  callosum  with  a  pair  of  bhmt  pointed 
forceps;  this  operation  had  better  be  commenced  in  the 
region  of  the  caudal  extremity  of  the  ventricle,  where  the 
fasciculus  is  quite  distinct  and  well  developed.  This  fascic- 
ulus begins  at  the  cornu  anterius  ventriculi  lateralis  as  a 
very  slender  band  of  substantia  alba,  which  in  some  in- 
stances can  with  difficulty  be  traced — attached  to  the 
nucleus  caudatus— cephalad  and  ventrad  to  the  substantia 
perforata  anterior ;  or  it  may  run  into  the  radix  olf actorius 
intermedia. 

An  earnest  effort  should  be  made  to  accomplish  this 
dissection,  as  some  variation  in  the  cephalic  termination  of 
the  fasciculus  subcallosus  may  be  ascertained.  As  the  fascic- 
ulus is  traced  caudad  it  becomes  wider  and  thicker,  form- 
ing a  very  graceful  band  having  the  shape  of  the  italic 
letter  /;  passing  dorsad  to  the  caudal  extremity  of  the 
corpus  striatum,  the  plexus  chorioideus  ventriculi  lateralis, 
the  hippocampus,  and  the  dorsal  portion  of  the  cornu  in- 
lerius  ventriculi  lateralis.  Traced  farther  caudad,  it 
passes  between  the  fibres  of  the  splenium,  and  those  of  the 
cingulum  superius,  and  finally  spreads  out  in  a  radiating 
manner  to  be  distributed  to  the  caudal  extremity  of  the 
pallium. 

Particular  attention  must  be  given  to  the  manner  in 
which  the  caudal  extremities  of  the  cingulum  superior, 
the  splenium,  and  the  fasciculus  subcallosus  are  related  to 
each  other.  The  fasciculus  subcallosus  forms  a  very  small 
portion  of  the  roof  of  the  ventriculus  lateralis  along  its 
lateral  aspect;  and  as  it  passes  cephalad  it  winds  around 
the  nucleus  caudatus.  Traced  caudad  it  forms  more  of 
the  roof  of  the  ventricle  and  when  it  arches  over  the  cornu 
inferius  ventriculi  lateralis  it  is  quite  wide  and  easily 
identified. 

The  ventral  surface  of  the  fasciculus  subcallosus  is  cov- 
ered by  the  ependyma  which  lines  the  general  ventricular 
cavity  of  the  encephalon,  while  its  dorsal  surface  is  in  con- 
tact with  the  substance  of  the  corpus  callosum,  and  the 
substantia  filba  of  the  overlying  pallium. 


60  ANATOMY    OF   THE   BRAIN 

The  cinguluin  superior  and  the  fasciculus  subcallosus, 
are  structures  that  may  be  called  association  bundles,  be- 
cause they  connect  different  regions  of  the  same  hemi- 
sphere. Some  of  these  bundles  are  quite  long,  connect- 
ing for  example,  the  polus  anticus  with  the  polus  posticus ; 
while  other  bundles  may  be  very  short,  connecting  contigu- 
ous gyri.  These  association  bundles  contain  both  cortici- 
fugal  and  corticipetal  axones. 

Make  another  incision  in  the  corpus  callosum,  parallel 
to  that  already  made,  exposing  the  one  ventricle  and  2  mm. 
to  the  opposite  side,  leaving  a  small  strip  of  corpus  callosum 
in  the  middle  line;  carefully  reflect  the  corpus  callosum 
just  cut  through,  from  over  the  remaining  ventriculus 
lateralis,  and  the  two  ventricles  will  be  clearly  exposed  to 
view.  Now  proceed  to  open  the  whole  of  the  body  of  the 
ventricle,  by  removing  the  remaining  portions  of  the  corpus 
callosum  except  the  central  sagittal  strip,  the  genu,  and 
above  4  mm.  of  the  splenium. 


ANATOMY    OF    THE    BRAIN  61 

CHAPTER  XV. 

THE  LATERAL  VENTRICLES. 

The  ventriculi  laterales  (Plates  XIII,  XIV,  XV,  XVI, 
XVII,  XXVI  fig.  2,  XXVII,  and  XXVIII  figs.  1  and  2) 
are  two  symmetrically  arranged  cavities,  one  for  each 
hemisphferium.  These  ventricles  are  large  irregular  cavi- 
ties lined  -with  ependyma.  a  species  of  epithelimn  derived 
from  the  original  cell  layer  of  the  embryonic  neural  tube. 
This  epend%nna  lines  all  the  ventricles  of  the  eneephalon 
and  is  reflected  over  the  pia  mater  and  the  plexus  chor- 
ioideus  that  lie  in  these  cavities,  and,  at  the  caudal  ex- 
tremity of  the  ventriculus  quartus.  it  becomes  continuous 
with  the  ependyma  lining  the  canalis  centralis  of  the 
medulla  spinalis. 

Each  ventriculus  lateralis  is  about  3  cm.  long,  8  mm. 
wide,  and  about  6  mm.  at  its  greatest  depth.  The  roof  is 
formed  principally  by  the  transverse  fibres  of  the  corpus 
eallosum :  the  fasciculus  subeallosus.  however,  as  previously 
stated,  enters  in  a  small  measure  into  the  formation  of  the 
roof  of  the  ventricle  at  its  caudo-lateral  portion.  Its 
cephalic  wall  is  formed  by  the  genu.  The  mesial  portion 
of  the  caudal  extremity  of  the  ventricle  in  the  middle  line 
is  lost  in  the  angle  formed  by  the  union  of  the  fornix  with 
the  corpus  eallosum.  while  the  lateral  portion  is  carried 
ventro-laterad  as  the  cornu  inferius  ventriculi  lateralis. 

The  floor  of  the  ventricle  is  very  irregular  and  is  formed 
by  the  following  structures:  Caput  nuclei  caudaii,  plexus 
chorioideus  veniricidi  lateralis,  corpus  fornicis,  and  hip- 
pocampus. 

Filling  in  the  concavity  of  the  genu  corporis  callosi,  is 
a  thin  membrane,  the  septum  pellucidum,  which  separates 
the  two  ventriculi  laterales  toward  their  cephalic  extremi- 
ties. The  septum  pellucidum  is  thin  and  translucent,  and 
extends  from  the  inner  concave  surface  of  the  corpus  cal- 
lorum  to  the  columnae  fornicis  anterior es. 

In  an  occasional  specimen  the  two  layers  which  go  to 


62  ANATOMY    OF    THE    BRAIN 

make  the  septum  pelliicidum,  can  be  demonstrated,  with 
a  very  narroAv  space  intervening;  the  so-called  fifth  ven- 
tricle or  pseudocode.  This  cavum  septi  pelludici  is  located 
in  the  cephalic  part  of  the  septum  close  to  the  colulnnae 
fornicis.  A  small  vessel  can  be  seen  in  this  cavity,  which  is 
derived  from  the  vessels  on  the  ventral  surface  of  the 
encephalon. 

In  most  instances,  however,  the  septum  is  so  thin  that 
it  appears  to  consist  only  of  the  double  layer  of  the  epen- 
dyma.  In}  several  specimens,  however,  the  ventral  part 
of  the  septum  pellucidum  could  be  seen  to  consist  of  two 
layers  of  tissue,  between  which  was  a  very  narrow  slit-like 
space,  that  extended  for  some  distance  caudad. 

Leading  from  the  main  cavity  of  each  ventriculus  later- 
alis are  two  quite  large  prolongations  called  the  cornua. 

The  cornu  anterius  ventriculi  lateralis  projects  ceph- 
alad,  ventrad,  and  somewhat  laterad  around  the  cephalic 
extremity  of  the  caput  nuclei  caudati  to  its  ventral  ex- 
tremity, where,  turning  sharply  cephalad,  it  enters  the 
tractus,  and  passes  thence  to  the  bulbus  oifactorius  to  form 
the  ventriculus  hulhi  olfactorii. 

The  cornu  inferius  ventriculi  lateralis  is  in  reality  the 
continuation,  ventrad  and  cephalad,  of  the  caudo-laterad 
extremity  of  the  ventricle.  This  cornu  toward  its  termina- 
tion bends  mediad,  and  terminates  opposite  a  point  on  the 
ventral  surface  of  the  encephalon  where  the  tractus  opticus 
passes  dorsad  to  the  lobus  hippocampi. 

Passing  into  this  cornu  are  seen  the  hippocampus,  fim- 
bria hippocampi  (tania  hippocampi),  fascia  dentata,  and 
the  plexus  chorioideus  ventriculi  lateralis  (Plate  XVI). 

The  portion  of  the  encephalon  forming  the  outer  wall  of 
the  descending  cornu  should  be  removed  from  one  side, 
exposing  the  entire  cavity  and  its  contents,  care  being 
taken  not  to  disturb  the  hippocampus  and  the  plexus. 

At  the  caudal  extremity  of  the  ventriculus  lateralis, 
where  the  hippocampus  takes  a  sharp  turn  ventrad,  there 
can  be  seen  in  most  instances,  a  shallow  cavity  pointing 
caudad;  this  depression  is,  in  all  probability,  a  poorly  de- 


ANATOMY    OF    THE    BRAIN  63 

veloped   coruu   posterius   ventriculi   lateralis,    so   well   de- 
veloped in  the  human  eneephalon. 

In  the  further  consideration  of  the  ventrieulus  lateralis, 
it  would  be  well  to  study  the  structures  lying  in,  or  form- 
ing the  floor  of  the  cavity. 

The  intraventricular  portion  of  the  corpus  striatum 
called  the  nucleus  caudatus,  is  the  large  pear-shaped  pro- 
jection more  readily  seen  in  the  cephalic  extremity  of  the 
cavity.  It  is  composed  of  substantia  grisea  covered  by  the 
ependyma  lining  of  the  ventricle.  Over  its  convex  surface 
are  seen  quite  a  number  of  large  veins  that  meet  near  the 
union  of  the  middle  and  caudal  thirds  of  its  inner  border, 
forming  one  large  vena  terminalis,  into  which  empties  the 
V.  chorioidea. 

The  V.  terminalis  leaves  the  ventrieulus  lateralis  through 
the  foramen  interventriculare  (foramen  of  Monro,  porta) 
(Plates  XIII,  XIV,  XV  and  Fig  D),  and  enters  the  ven- 
trieulus tertius  where  it  becomes  the  V.  cerehri  interna. 

The  further  course  of  this  vein  will  be  followed  when 
the  structures  of  the  ventrieulus  tertius  are  considered. 

The  internal  arrangement  and  relationships  of  the  struc- 
tures forming  the  corpus  striatum  will  be  exposed  and 
studied  after  the  other  prominent  features  of  the  ventrie- 
ulus lateralis  have  been  considered. 

At  the  point  Avhere  the  V,  terminalis  dips  ventrad  to 
reach  the  foramen  interventriculare  will  be  seen  a  tri- 
angular space  called  the  recessus  triangularis ;  this  space 
is  very  apparent  if  the  corpus  fornicis  and  the  nucleus 
caudatus  be  slightly  separated. 

Lying  against  the  caudal  two-thirds  of  the  internal  sur- 
face of  the  nucleus  caudatus  is  the  plexns  ckorioideus  ven- 
triculi lateralis,  a  very  dense  vascular  fringe  formed  on 
the  margin  of  that  portion  of  pia  mater  which  pushes 
the  very  thin  wall  of  the  ventricle  before  it  during  devel- 
opment, and  finally  occupies  the  fissura  transversa.  On 
superficial  examination  this  plexus  appears  to  lie  within 
the  ventricular  cavity  of  the  eneephalon  though  morpho- 
logically it  is  outside  of  it. 

This  process  of  pia  as  it  rests  over  the  third  ventricle  is 


64  ANATOMY   OF    THE   BRAIN 

called  the  tela  chorioidea  ventriculi  tertii  (velum  inter- 
positum). 

The  plexus  ehorioideus  ventriculi  lateralis,  traced 
cephalad,  apparently  leaves  the  ventriculus  lateralis  pass- 
ing into  the  ventriculus  tertius  by  way  of  the  foramen 
interventriculare ;  then  proceeding  caudad  on  the  ventral 
surface  of  the  tela,  it  forms  the  plexus  ehorioideus  ven- 
triculi tertii. 

Now  note  particularly,  that  at  every  point  in  its  course, 
the  plexus  ehorioideus  is  always  covered  by  the  thin  ven- 
tricular wall  which  is  not  visible  to  the  naked  eye,  and  al- 
ways morphologically  outside  of  both  the  foramen  inter- 
ventriculare and  the  ventricle. 

Reflect  the  sagittal  strip  of  corpus  callosum  remaining 
after  exposing  the  ventriculi  laterales,  and  the  fornix  will 
be  seen;  in  removing  this  strip,  do  not  in  any  way  molest 
the  genu.  The  septum  pellucidum  can  now  be  very  nicely 
seen  (Plate  XIV),  stretching  between  the  genu  corporis 
callosi  and  the  columnae  f ornicis ;  examine  the  septum  care- 
fully at  this  stage  and  see  if  two  laminas  can  be  demon- 
strated. Tracing  the  plexus  ehorioideus  ventriculi  lateralis 
caudad  and  laterad,  it  will  be  seen  to  pass  ventrad,  accom- 
panying the  cornu  inferius  ventriculi  lateralis  and  follow- 
ing the  concave  border  of  the  hippocampus  almost  to  the 
extremity  of  the  cornu. 

The  plexus  receives  its  arterial  supply  from  the  ramus 
posticus  of  the  A.  cerebri  propria  and  from  the  A.  cerebri 
posterior. 


ANATOMY   OF   THE   BRAIN  65 


CHAPTER  XVI. 


THE  FORNIX. 

The  corpus  fornicis  (L.,  fornix,  an  arch)  (Plates  XIII, 
XIV,  XVI,  XX,  XXVII)  is  a  large  body  of  substantia 
alba,  triangular  in  shape,  and  attached  to  the  ventral  sur- 
face of  the  caudal  half  of  the  corpus  callosum. 

Stretching  along  either  side  of  the  fornix  is  tho  plexus 
chorioideus  ventriculi  lateralis. 

At  its  cephalic  extremity  the  fornix  is  continued  as  two 
large  cords  of  tissue  called  the  columnae  fornicis  which 
dip  ventrad  and  then  caudad  to  end  in  the  corpora  mamil- 
laria,  as  shown  in  Plate  XX. 

The  course  of  these  columnae  will  be  shown  when  work- 
ing out  the  structures  on  the  facies  medialis  cerebri. 

The  central  portion  of  the  corpus  fornicis  runs  caudad 
between  the  dorsal  extremities  of  the  hippocampi,  forming 
the  commissura  hippocampi.  Some  fibres  at  the  cephalic 
extremity  of  the  commissura  hippocampi  run  in  a  sagittal 
direction,  filling  in  the  angle  formed  by  the  diverging  crura 
fornicis  posterioria  (posterior  pillars  of  the  fornix)  as  they 
approach  the  hippocampi.  These  sagittal  fibres,  on  reach- 
ing the  caudal  border  of  the  splenium,  divide  into  two 
bundles,  one  proceeding  toward  each  polus  occipitalis  cere- 
bri. 

Pick  up  some  of  these  mesial  sagittal  fibres  of  the  fornix 
and  tracing  them  caudad,  they  will  be  seen  to  diverge,  and 
run  with  the  transverse  fibres  of  the  splenium. 

No  little  difficulty  will  be  experienced  in  tracing  the 
fibres  of  the  various  fasciculi  of  the  fornix  even  if  great 
care  is  exercised  in  making  the  dissection.  Furthermore, 
some  fibres  will  be  found  to  unite  with  the  substantia  alba 
of  the  hippocampi. 

The  marginal  strands  pass  latero-caudad  to  reach  the 
concave  borders  of  the  hippocampi,  where  they  are  called 
the  fimhria  hippocampi  CfOJ'pus  fimbriatum,  taenia  hip- 
pocampi), along  which  they  can  be  traced  almost  to  the 


66  ANATOMY   OF   THE   BRAIN 

extremity  of  the  ventricle  (Plates  XIV,  XVI,  XXVIII). 
As  each  timbria  runs  into  the  cornu  inferius  ventriculi 
lateralis,  it  gradually  diminishes  in  size  and  is  finally  lost 
on  the  free  concave  border  of  the  hippocampus. 

The  student  should  take  ample  time  to  study  the  rela- 
tionship of  the  fornix  to  the  surrounding  structures,  as 
well  as  its  attachments  with  the  hippocampi  and  the  cor- 
pora mamillaria.  Note  the  exact  position  of  the  columnae 
fornicis  in  their  relations  to  the  commissura  anterior,  the 
ventriculus  tertius,  the  foramen  interventriculare  and  the 
ventriculi  laterales. 

The  continuity  of  the  columnae  fornicis  with  the  cor- 
pora mamillaria  will  be  worked  out  in  a  later  dissection. 

Make  special  note  of  the  relative  position  of  the  fol- 
lowing structures;  corpus  callosum,  fornix  and  velum 
interpositum,  and  their  proximity  to  the  ventricles. 


ANATO]\IY    OF    THE    BRAIN  67 


CHAPTER  XVII. 

THE  HIPPOCAMPUS. 
(Plates  XIII,  XIV,  XVI,  XXI,  XXII,  XXVIII) 

The  hippocampus  is  a  large  curved  cylindrical  body 
formed  by  the  fissura  defitata  (Plate  XVII)  projecting 
into  the  caudal  portion  of  the  ventriculus  lateralis  and 
its  cornu  inf erius ;  it  begins  in  the  caudal  third  of  the  floor 
of  the  ventricle,  and  at  once  passes  into  the  cornu.  Its 
direction  at  its  beginning  is  latero-caudad,  but  it  changes 
its  course  very  abruptly  and  dips  into  the  cornu  inferius  al- 
most vertically ;  toward  its  termination  it  changes  its  course 
again,  running  in  a  cephalo-mediad  direction,  and  ends  at 
the  extremity  of  the  cornu  inferius  ventriculi  lateralis,  at 
about  the  cephalic  pole  of  the  lobus  hippocampi. 

The  substantia  grisea  of  the  lobus  hippocampi  can  now 
be  traced  around  the  ventro-mesial  border  of  the  lobe  to  its 
inner  surface. 

At  this  stage  of  the  dissection  make  a  transverse  incision 
through  the  cephalic  extremity  of  the  corpus  fornicis  just 
at  the  dorsal  end  of  the  forajiien  interventriculare.  Make 
another  incision  through  the  tractus  olfactorius  where  it 
joins  the  lobus  hippocampi  using  the  side  of  the  eneephalon 
where  the  external  wall  of  the  cornu  inferius  has  already 
been  removed  in  a  previous  stage.  Now  proceed  to  ele- 
vate the  corpus  fornicis  and  the  hippocampus  which  is 
cut  loose  from  its  tractus  olfactorius,  avoiding  injury  to 
the  delicate  tela  chorioidea  ventriculi  tertii,  and  its  plexus. 

The  tela  will  be  seen  to  pass  laterad,  ventrad  and 
cephalad,  and  rests  in  the  fissura  transversa  cerebri.  This 
fissure  will  be  seen  between  the  following  structures,  viz., 
the  fornix,  splenium  and  hippocampus  dorsad  and  laterad, 
and  the  corpora  quadrigemina,  pendunculi  cerebri  and  the 
thalami,  ventrad  and  mesiad.  The  fissure  is  horseshoe- 
shaped  and  lies  in  a  plane  which  cuts  the  horizontal  at 
about  70°. 

As  previously  staterl,  the  pia  mater  invaginates  the  cavity 


68  ANATOMY   OF   THE   BEAIN 

of  the  encephalon  through  the  flssura  transversa  cerebri 
where  it  forms  the  tela  chorioidea  ventriculi  tertii.  Care 
should  be  exercised  so  that  the"  location  and  relations  of  this 
fissure  are  clearly  understood.  If  the  thin  wall  of  the 
encephalon,  which  is  pushed  into  the  ventricular  cavity 
during  development,  were  visible,  there  would  be  little 
difficulty  in  understanding  the  true  relationship  of  the 
various  structures  in  this  neighborhood ;  and  how  it  is  that 
the  choroid  plexus  is  not  inside  the  cavity  of  the  ventricles, 
nor  the  foramen  interventriculare  a  true  foramen  nor  the 
fissura  transversa  a  true  fissure,  in  the  sense  that  they  open 
into  the  ventricular  cavities. 

In  turning  again  to  the  substantia  grisea  of  the  lobus 
olfactorius  (hippocampi)  it  will  be  seen  to  pass  to  the  con- 
cave surface  of  the  hippocampus  where  the  fissura  hippo- 
campi (fissura  dentata)  lies  parallel  to  the  margin  of  the 
fimbria  hippocampi;  the  fold  of  substantia  grisea  lying  be- 
tween the  fissura  hippocampi  and  the  fimjbia  is  the  fascia 
dentata  hippocampi  (Plates  XVII,  XXVIII,  figs.  1  and  2). 

The  substantia  grisea  which  surrounds  the  fissura  hippo- 
campi can  be  traced  dorsad,  mediad  and  cephalad  where  it 
finally  ends  in  the  fasciola  cinerea.  (Plates  VIII,  XVIII, 
XXVIII,  fig.  1)  close  to  the  middle  line  where  only  a  nar- 
row slit  separates  it  from  the  fasciola  of  the  opposite  hip- 
pocampus. The  fissura  hippocampi  can  be  distinctly  traced 
to,  and  around  the  dorsal  extremity  of  the  fasciola  to  its 
mesial  surface  where  it  ends.  Each  fasciola  is  thus  divided 
into  a  dorsal  part  continuous  with  the  fascia  dentata,  and 
a  ventral  part  continuous  with  the  substantia  grisea  of  the 
hippocampus.  None  of  the  fibres  of  the  fimbria  can  be 
traced  to  the  ventral  portion  of  the  fasciola.  Pick  up  some 
of  the  fibres  of  the  ventral  surface  of  the  fornix,  and  many 
can  be  traced  very  nicely,  to  the  fasciola  cinerea  and  the 
substantia  grisea  of  the  fascia  dentata;  while  the  fibres  of 
the  fimbria  hippocampi  are  distinctly  distributed  to  the 
fascia  dentata  only. 

Turn  the  severed  hippocampus  over  to  the  opposite  side 
together  with  the  fornix ;  this  will  expose  the  tela  chorioidea 


ANATOMY   OF    THE   BRAIN  69 

ventrieiili  tertii  lying  dorsad  to  the  caudal  half  of  the  ven- 
triculus  tertiiis. 

At  the  cephalic  extremity  "of  the  tela  the  Vv.  cerebri  in- 
temae  unite  to  form  a  large  central  vein,  the  V.  cerebri 
magna  (vein  of  Galen)  (Plates  III,  XIV)  which  runs  di- 
rectly caudad  to  the  middle  line  of  the  tela,  over  the  corpus 
pineale,  ventral  to  the  central  line  of  the  splenium  corporis 
callosi. 

At  this  point  the  vein  rests  in  the  sulcus  separating  the 
fasciolae  cinereae,  then  passing  caudad  about  1.5  cm.  it  en- 
ters the  sinus  sagittalis  as  described  when  studying  the 
sinuses. 

Grasp  the  cephalic  extremity  of  the  V.  cerebri  magna 
and  pull  it  and  the  tela,  caudad,  in  order  to  expose  the  ven- 
tral surface  of  the  tela.  On  each  side  of  this  vein  will  be 
seen  the  plexus  chorioideus  ventriculi  tertii. 

Now  replace  the  vena  magna  with  the  tela,  and  note  the 
following  structures.  Mediad  to  the  place  occupied  by  the 
plexus  chorioideus  ventriculi  lateralis  on  either  side,  will 
be  found  a  large  oval  eminence,  the  thalamus;  between  the 
caudal  extremities  of  the  thai  ami  there  lies  a  small  conical 
body,  the  corpus  pineale  (Plates  XV  and  XXVII,  fig.  2). 
Caudad  to  the  thalami  and  the  corpus  pineale  are  four 
eminences  or  collieuli  called  the  corpora  quadrigennina 
(Plates  XV,  XXI,  XXIV,  and  XXV).  Reflect  the  tela 
from  these  four  bodies  and  its  continuation  with  the  pia 
that  is  attached  to  the  outer  aspect  of  the  eneephalon  can 
be  easily  understod. 

The  large  V.  cerebri  posterior  will  be  seen  in  the  groove 
between  the  thalamus  and  the  corpora  quadrigemina ;  it 
runs  dorsad  and  empties  into  the  V.  cerebri  magna  as  it  lies 
between  the  caudal  extremities  of  the  hemisphseria  cerebri. 

By  gently  separating  the  corpus  striatum  (nucleus  cau- 
datiLs)  from  the  thalamus,  the  stria  temiinalis  (taenia  semi- 
circularis)  (Plate  XVI)  will  be  seen  at  the  bottom  of  the 
sulcus  separating  these  two  structures.  It  consists  of  white 
fibres  that  end  cephalad  in  the  caput  of  the  corresponding 
nucleus  candatus  and  caudad  they  follow  the  cauda  of  the 
nucleus  caudatus  to  its  end. 


70  ANATOMY    OF    THE    BRAIN 


CHAPTER  XVIII. 

THE  OPTIC  THALAMUS. 

The  thalamus  opticus  (for  illustrations  see  Plate  XV)  is 
not  seen  when  the  corpus  callosum  is  removed  to  expose 
the  ventriculus  lateralis.  In  order  to  see  it,  the  plexus 
ehorioideus  lateralis  must  be  pulled  toward  the  fornix,  and 
the  edge  of  the  latter  structure  somewhat  elevated;  this 
maneuver  will  expose  the  thalamus  very  clearly,  and  show 
at  a  glance  its  relations  to  the  corpus  striatum,  fornix  and 
plexus  ehorioideus. 

In  the  human  encephalon,  the  thalamub  is  exposed  to 
view  as  soon  as  the  corpus  callosum  is  removed. 

At  the  present  stage  of  the  dissection,  however,  the  free 
surfaces  of  the  thalami  are  nicely  exposed,  with  the  excep- 
tion of  the  mesial ;  which,  however,"  was  identified  and 
briefly  described  when  studying  the  facies  mediaMs  cerebri 
(Plate  VIII). 

As  can  readily  be  seen,  a  large  pavt  of  the  cephalo-mesial 
surface  of  one  thalamus  is  attached  to  the  corresponding 
part  of  the  mesial  surface  of  the  opposite  thalamus,  form- 
ing a  bridge  across  the  cavity  of  the  ventriculus  tertius ; 
this  can  be  the  better  seen  if  a  very  slight  effort,  not  suf- 
ficiently violent  to  rupture  the  connection,  be  made  to  sep- 
arate the  two  thalami.  This  bridge  consists  of  substantia 
grisea,  and  is  called  the  massa  intermedia,  the  so-called 
middle  commissure— a  misuse  of  the  term  commissure. 

Near  the  mesial  border  of  the  dorsal  surface  of  each 
thalamus  will  be  seen  the  stria  medullaris  thalami  to  be  de- 
scribed later.  The  thalamus  appears  to  terminate  caudad 
in  a  large  projection  or  tubercle  called  the  j^ulvinar  (tuber- 
culum  thalami  posterius).  A  similar  protuberance,  though 
smaller  and  much  less  prominent  can  usually  be  seen  on 
the  cephalic  extremity  of  the  thalamus  which  has  been 
named  the  tiiherculum  thalami  anterius,  to  which  can  be 
traced  the  fasciculus  thalamomamillare  at  its  dorsal  ex- 
tremity. 


AXATOMY    OF    THE    BRAIX  71 

Just  beneath  the  pulvinar  and  a  little  laterad  is  the  cor- 
pus geniculatum  internum.  The  corpus  genicidatum  ex- 
ternum (Plate  XXXVIII)  will  be  noticed  in  close  relation 
with  the  corpus  geniculatum  internum  lying  directly 
cephalad  and  a  little  dorsad,  the  point  of  the  line  0  (Plate 
XXI)  shows  the  location  of  this  body  which  is  very  in- 
distinct in  fresh  specimens. 

In  a  subsequent  dissection,  after  the  structures  exposed 
in  Plate  XXI  have  been  studied,  cut  deeply  into  the  tractus 
opticus  and  the  corpora  geniculata  at  right  angles  to  the 
surface,  the  direction  of  the  incision  to  pass  through  the 
tips  of  the  lines  G  and  F.  This  section  will  expose  the 
substance  of  the  two  geniculate  bodies  and  show  them  sep- 
arated by  only  a  very  thin  layer  of  substantia  alba.  This 
substantia  alba  appears  to  form  more  or  less  of  a  capsule 
that  in  many  instances  can  be  observed  to  completely  sur- 
round the  substantia  grisea  of  the  external  geniculate 
bodies. 

Later,  the  tractus  opticus  will  be  traced  to  the  pulvinar. 
the  corpus  geniculatum  externum  and  to  one  of  the  cephalic 
pair  of  the  corpora  quadrigemina  (colliculus  superior).  We 
may  now  revert  to  a  brief  consideration  of  the  corpus 
striatum  together  with  a  short  study  of  some  of  the  ar- 
rangements of  the  constituents  of  the  thalamus. 

Make  a  horizontal  section  through  the  entire  hemi- 
sphaerium  cerebri  to  which  the  lobus  olfactorius  is  still  at- 
tached, just  dorsad  to  the  sulcus  rhinalis,  carrying  the  in- 
cision to  the  middle  line  with  one  sweep  of  the  brain-knife 
and  study  the  structures  exposed  as  shown  in  Plate  XVIII. 

The  substantia  grisea  of  the  nucleus  caudatus  is  easily 
identified ;  external  to  this  is  a  more  or  less  interrupted  band 
of  substantia  alba,  the  capsula  interna. 

Beginning  at  its  cephalic  extremity  this  capsule  is  di- 
rected mediad  and  caudad,  until  it  reaches  the  sulcus  lying 
between  the  thalamus  and  the  nucleus  caudatus;  at  this 
point  it  makes  a  bend  called  the  ge7iu  capsuloE  internee  and 
then  proceeds  laterad  and  caudad  as  a  dense  white  band 
ending  finally  in  the  substantia  alba  of  the  occipital  ex- 
tremity of  the  hemisphere. 


72  ANATOMY   OF    THE   BRAIN 

That  part  of  the  capsule  lying-  cephalad  to  the  genu  is 
called  the  pars  frontalis  (anterior  limb),  while  that  portion 
caudad  to  the  genu  is  the  pars  postica  (posterior  limb). 

Lying  directly  external  to  the  capsula  interna  is  the 
nucleus  lentiformis  (nucleus  lenticularis).  In  many  cases 
this  nucleus  lentiformis  can  be  seen  to  be  composed  of  an 
external  dark  portion,  the  putamen,  and  an  internal  part, 
lighter  in  color,  called  the  globus  pallidus. 

External  to  the  nucleus  lentiformis  is  seen  a  very  thin 
band  of  substantia  alba,  the  capsula,  externa,  connecting 
the  substantia  alba  of  the  lobus  frontalis  with  the  substantia 
alba  of  the  lobus  occipitalis. 

Laterad  to  the  capsula  externa  is  the  claustrum  (clau- 
DEBE,  to  shut),  an  irregular  band  of  substantia  grisea; 
varying  in  amount  and  in  some  specimens  difficult  to 
demonstrate. 

Lying  immediately  outside  the  claustrum  is  the  substantia 
alba,  very  small  in  quantity,  and  the  substantia  grisea,  very 
considerable  in  quantity,  of  the  insula.  The  substantia 
grisea  of  the  insula  is  cortical  matter,  and  is  directly  con- 
tinuous with  the  general  cortical  substance  of  the  ence- 
phalon. 

The  surface  lying  internal  to  the  pars  postica  of  the 
capsula  interna,  is  the  cut  surface  of  the  thalamus,  con- 
sisting of  substantia  alba  and  substantia  grisea  arranged  in 
a  very  interesting  manner  as  follows: 

The  substantia  alba  is  centrally  located,  shaped  like  a  tri- 
angle, the  sides  of  which  are  slightly  concave,  and  which 
might  be  called  the  pars  centi^alis  thalami.  The  pars  cen- 
tralis divides  the  substantia  grisea  of  the  thalamus  into 
three  distinct  areas;  the  area  medialis  thalami,  the  largest 
of  the  three  portions  of  the  substantia  grisea,  which  lies 
between  the  pars  centralis  thalami  and  the  mesial  surface 
of  the  thalamus ;  the  area  lateralis  thalami  is  between 
the  pars  centralis  thalami  and  the  pars  postica  of  the  cap- 
sula interna;  the  area  posterior  thalami  is  located  di- 
rectly caudad  to  the  pars  centralis  thalami,  forming  the 
caudal  extremity  of  the  thalamus  and  enters  largely  into 
the  formation  of  the  pulvinar. 


ANATOMY    OF    IHE   BRAIN  73 

The  area  posterior  thalami  is  occasionally  very  plainly 
divided  into  two  portions  of  nearly  equal  size  by  a  sagittally 
directed  process  of  substantia  alba  derived  from  the  pars 
centralis  and  extending  eaudad. 

The  arrangement  of  the  substantia  alba  and  the  substan- 
tia grisea  just  described  can  be  very  nicely  seen  if  the  en- 
eephalon  be  prepai-ed  by  the  Kaiserling  method.* 

In  this  description  of  the  gray  and  white  masses  of  the 
thalamus,  no  attempt  is  made  to  homologize  them  with  the 
several  nuclei  of  the  thalamus  opticus  of  man.*   (**) 

The  instructor  should  prepare  a  number  of  encephala 


*The  Kaiserling  Method. — A  method  for  "wet  preparations"  of  the  central 
neiTous  system  for  museum  and  demonstration  specimens.  It  results  in  a  speci- 
men tough  enough  to  resist  much  handling,  and  at  the  same  time  one  in  which 
both  the  normal  size  and  especially  the  color  are  retained  to  aj  remarkable  degree. 
It  is  well  adapted   for   pathological  specimens,   whether  of   nervous  or   other   tissue. 

Special  Reagents  Required. 

A.  Fixing  and  hardening  fluid — 

Formalin    (40    per    cent    formaldehyde) cc.     200 

Distilled    water     cc.  1000 

Potassium    nitrate     (saltpetre) grama       15 

Potassium    acetate     grams       30 

B.  Preserving  fluid — - 

Potassium    acetate     grams     200 

Glycerine     cc.     400 

Distilled    water    cc.  2000 

The  formulae  as  given  will  result  in  fluids  sufficient  in  amount  for  a 
human    brain,    provided    the    vessels    used    are    small    enough. 

Procedure. 

1.  The  brain  or  spinal  cord  is  removed  and  placed  in  a  vessel  containing 
enough  of  the  fixing  fluid  A  to  cover  it  well,  keeping  it  in  the  dark  for  from 
six    to    eight    days. 

It  Ib  advisable  to  inject  about  400  cc.  of  the  fluid  through  the  internal 
carotid  artery  before  removing  the  brain,  especially  if  there  is  reason  to  be- 
lieve that  post-mortem  softening  has  begun.  Do  not  inject  too  much,  lest 
the  blood,   and  consequentlv  the  color,  be  washed  out  of  the  blood-vessels. 

The  bottom  of  the  vessel  should  be  padded  with  absorbent  cotton,  and 
during  the  period  of  fixation,  the  position  of  the  specimen,  should  be  changed 
from    time   to    time   to   prevent   flattening   or   distortion. 

2.  Drain  the  specimen  for  2  or  3  minutes,  and  place  in  95  per  cent  alco- 
hol  for  5  or   0   hours. 

3.  Then  place  in  a  glass  vessel  containing  the  preserving  fluid  B,  where  it 
will  keep  indefinitely. 

Even  in  the  preserving  fluid  it  is  advised  to  keep  the  preparation  in  the 
dark  as  much  as  possible,  since  the  long  exposure  to  light  seems  to  cause  it  to 
lose  its  natural  color. 

When  on  exhibition  or  in  use  for  study  or  demonstration,  the  preparation 
may  be  improved  in  appearance  by  placing  it  in  80  per  cent  alcohol  for  the 
time  being.  This  seems  to  brighten  the  color  to  a  certain  extent.  Too  long 
duration    in    alcohol,    however,    will    extract    the    color. 

ThiH  process  is  well  adapted  for  the  preparation  of  specimens  for  dissec- 
tion. If  dissection  is  made,  it  is  suggested  that  it  should  be  delayed  until 
aft«;r  the  specimen  has  been  in  the  preserving  fluid  for  about  two  wccks.^ — 
"Virchow'B    Archiv."     Bd.    147,    Heft.    3,    p.    389.    1897. 


•  (**)  A  very  conci.se  iiiid  dear  ilfscripi  ion  nf  (lie  hnrnnn  th:il:itiuis  is  givni  \>y 
GuBtav  Mann,  M.  D.  Kdin.,  B.  So.  Oxon.,  in  The  British  Medical  Journal 
Feb.    11,    1905. 


74  ANATOMY   OF   THE   BRAIN 

by  the  Kaiserling  process  and  make  the  necessary  dis- 
section^ to  show  these  structures  for  verifying  the  text; 
as  brains  prepared  simply  in  formalin  occasionally  do  not 
show  the  differentiation,  or  at  best,  somewhat  indistinctly. 


ANATOMY    OF    THE   BRAIN  75 

CHAPTER  XIX. 

THE   PINEAL  BODY. 

The  corpus  pineale  (L.  Pinus,  a  pine-cone,  conarium, 
pineal  gland,  epiphysis).  Descartes  considered  this  struc- 
ture the  seat  of  the  soul.  (Plates  VIII,  XV,  XXV, 
XXVIII,  hg.  1.)  It  is  situated  in  the  fossa  formed  by  the 
eoUiculi  superiores  and  the  thai  ami. 

The  corpus  pineale  is  said  to  contain  neither  neuron  ele- 
ments nor  nerve  fibres.  It  does  contain,  however,  a  vari- 
able amount  of  hard,  gritty,  calcareous  grains  or  particles. 
Beware  of  this  material  if  sectioning  this  oi-gan  with  a  fine 
microtome  knife. 

Beneath  the  corpus  pineale  will  be  observed  quite  an 
acute  triangular  depression  which  may  be  called  the  fossa 
suhpinealis,  the  floor  of  which  is  formed  by  the  lamina 
pinealis.  Dorsal  to  the  corpus  passes  the  tela  chorioidea 
ventriculi  tertii  and  the  V.  cerebri  magna.  It  is  retained 
in  position  by  a  duplicate  of  pia,  derived  from  the  ventral 
surface  of  the  tela.  It  lies  dorsal  to  the  commissura  pos- 
terior. 

Leaving  the  ventral  surface  of  the  epiphysis  is  a  layer 
of  substantia  alba  called  the  lamma  pinealis  (Plate  XX) 
which  passes  caudad,  ventral  to  the  commissura  posterior 
and  ends  in  the  lamina  quadrigemina. 

Passing  across  the  dorsal  border  of  the  cephalic  surface 
of  the  corpus  pineale  is  a  short  transverse  band  of  tissue, 
called  the  commissura  liahemdarum  (habena,  a  rein  or  bit) 
ending   at    either   extremity    in    the    trigomim   liahenutiB. 

The  trigonum  habenulse  is  a  small  depression.  It  marks 
the  position  of  a  collection  of  cells  called  the  ganglion 
kahenulce.  Extending  from  this  ganglion,  making  a  grace- 
ful curve  in  a  caudo-ventral  direction  to  reach  the  nucleus 
interpeduncularis,  is  a  large  and  important  bundle  of 
fibres  called  the  fasciculus  retrofexus  of  Meynert.  This 
fasciculus  can  be  traced  very  easily  in  a  serial  section, 
stained  by  Pal-Weigert  process;  see  Plate  XXXVIII. 


76  ANATOMY   OF    THE   BRAIN 

Running  cephalad  from  the  trigonum  habenulai  on  either 
side  are  the  strice  medullares  thalami  (habenulae)  ;  these 
striffi  pass  cephalad,  resting  on  the  dorsal  border  of  the 
mesial  aspect  of  the  thalamus,  then  ventrad  until  they  reach 
the  neighborhood  of  the  foramen  interventriculare.  Their 
further  course  is  obscure.  Between  the  trigonum  habenula 
and  the  lamina  pinealis  will  be  seen  a  small  space  called  tht 
recessus  pinealis  ventriculi  tertii. 


ANATOMY    OF    THE   BRAIN  77 

CHAPTER  XX. 

THE  ANTERIOR  COMMISSURE. 

Press  the  columnaB  fornicis  gently  cephalad  and  you  will 
see  just  in  front  of  them,  as  they  diverge  in  their  course 
ventrad,  toward  the  ventral  part  of  ventriculus  tertius, 
a  large  transverse  cord  of  substantia  alba,  the  commissura 
anterior  cerebri  (Plate  VIII,  XVII,  XIX,  XX,  XXVII.) 
Take  a  lateral  half  of  the  eneephalon  and  scrape  away 
the  substantia  grisea  of  the  lobus  frontalis  in  the  region  of 
the  ventro-raesial  border,  and  that  of  the  nucleus  caudatus, 
taking  care  not  to  injure  the  columnas  fornicis,  and  expose 
the  lateral  prolongation  of  the  commissure. 

By  keeping  to  the  ventro-niesial  border  of  the  commissure 
as  the  student  proceeds  cephalad  there  Avill  be  no  fear  of 
injuring  any  important  structure  in  making  this  dissection. 
A  special  dissection  is  necessary  to  show  the  whole  of  the 
commissura  anterior  and  to  show  its  relations  to  the  bulbi 
olfactorii.  The  requisite  dissection  can  be  made  before  the 
eneephalon  has  been  cut  sagittally,  without  unduly  mutilat- 
ing the  lobi  f rontales,  as  follows . 

After  the  ventral  surface  of  the  brain  has  been  studied 
and  a  drawing  made,  including  the  chiasma  opticum  Math 
its  traeti  optici  and  the  nervi  optici,  the  search  for  the  com- 
missura can  be  undertaken.  With  a  sharp  scalpel  make  an 
incision  through  the  centre  of  the  chiasma  in  a  coronal  direc- 
tion, as  illustrated  in  Plate  XIX.  Now  proceed  with  some 
blunt  instrument  to  scrape  away  the  substantia  grisea  from 
the  loci  perforati  anteriores  to  the  extent  of  1  cm.  on  each 
side  of  the  fissura  longitudinalis  cerebri,  carrying  the  ex- 
cavation toward  the  dorsal  surface  of  the  eneephalon  until 
a  cord  of  substantia  alba  about  2  mm.  in  diameter  is 
reached ;  this  is  the  commissura  anterior.  The  further  dis- 
section is  carried  on  very  easily  when  once  this  point  is 
reached,  for  all  the  student  has  to  do  is  to  clear  away  the 
substantia  grisea  that  surrounds  the  remainder  of  the  struc- 


78  ANATOMY    OF   THE   BRAIN 

ture,  until  it  can  be  clearly  traced  from  one  bulbus  olfac- 
torius  to  the  other. 

The  commissura  is  horse-shoe-shaped,  with  its  centre 
about  1  cm.  immediately  dorsal  to  the  chiasma  optieum, 
while  the  limbs  run  cephalad,  parallel  to  the  fissura  longi- 
tudinalis,  and  enter  their  respective  bulbi  olfactorii. 

As  far  as  could  be  observed  from  gross  dissections,  the 
commissure  distributes  very  few  fibres  to  any  structures 
except  the  bulbi ;  a  few,  however,  appear  to  radiate  to  the 
lobi  frontales  and  the  lobi  temporales.  This  arrangement 
seems  to  be  quite  different  from  that  obtaining  in  the  brain 
of  man  where  the  major  portion  of  the  commissura  anterior 
is  distributed  to  the  lobi  temporales,  and  only  a  few  fibres 
to  the  bulbi  olfactorii.  On  no  account  should  the  study  of 
this  commissure  be  neglected. 

With  a  sharp  knife  cut  the  columna  fornicis,  on  the 
mesial  surface  of  a  lateral  half  of  an  encephalon,  at  the  for- 
amen interventrieulare,  and  gently  trace  it  cephalad  and 
ventrad.  At  the  point  where  the  columna  approaches  to 
within  about  .5  cm.  of  the  commissura  anterior,  it  is  called 
the  pars  libera  columnm  fornicis  as  shown  in  Plate  XX. 

When  it  reaches  the  level  of  the  commissura  it  becomes 
imbedded  in  a  quantity  of  substantia  grisea,  where  it  is 
called  the  pars  tecta  columnce  fornicis.  The  columna  is 
tough  and  is  composed  entirely  of  substantia  alba.  It 
passes  caudad  to  the  commissura  anterior  along  the  mesial 
border  of  the  thalamus  to  its  ventral  surface  to  reach  the 
corpus  mamillare,  where  it  is  distributed  to  the  substantia 
grisea  of  that  body.  A  very  nice  dissection  of  the  columna 
fornicis  can  be  made  by  simply  scraping  away  the  sub- 
stantia grisea  from  the  mesial  surface  that  covers  the  col- 
umna without  cutting  it. 

From  the  substantia  grisea  of  the  corpus  mamillare  there 
rises  a  cord  of  white  fibres  which  takes  a  course  cephalad, 
dorsad  and  then  slightly  caudad,  ending  in  the  nucleus 
of  the  tuberculum  anterius  thalami,  where  it  appears  to 
end  in  a  dense  spray  of  white  fibres  that  spread  out  and 
run  caudad  and  are  finally  lost  in  the  substance  of  the 
thalamus.     The  strand  that  connects  the  corpus  mamillare 


A.NATOMY    OF    THE    BRAIN  79 

with  the  thalamus  is  called  the  fasciculus  thalomomcmiil- 
laris  (tract  of  Yicq  d'Azyr). 

The  pars  teeta  columns  fornieis  and  the  fasciculus  thala- 
momaraillaris  are  quite  large  and  can  be  readily  exposed  if 
the  substantia  grisea  be  removed  as  directed.  To  show  the 
fasciculus  thalamomamillaris  the  excavation  must  be  car- 
ried caudad  until  a  large  part  of  the  surface  of  the  thala- 
mus has  been  removed.  In  no  ease  was  the  fasciculus  thala- 
momamillaris seen  to  be  directly  continuous  with  the  pars 
tecta  columns  fornieis,  in  the  substance  of  the  corpus 
raamillare.  In  making  the  incision  dividing  the  encephalon 
into  two  equal  parts,  the  knife  Avill  occasionally  deviate 
from  the  middle  line  as  it  approaches  the  ventral  surface, 
and  pass  down  through  the  ventral  portions  of  the  pars 
teeta  columnae  fornieis  and  fasciculus  thalamomamillaris, 
and  thus  expose  their  fibres  and  make  identification  easy. 


80  I  ANATOMY   OF   THE   BRAIN 


CHAPTER  XXI. 

THE  THIRD  VENTRICLE. 

The  ventriculus  tertius  (diacoele)  (Plates  XV,  XXV, 
XXVII,  XXVIII)  is  a  slit-like  space  in  the  central  region 
of  the  encephalon,  lying  in  the  sagittal  plane.  Overlying 
it  is  its  thin  roof  of  velum  interpositum  and  adherent  to 
this  is  the  tela  chorioidea  ventriculi  tertii. 

In  removing  the  brain  from  the  skull  the  V.  magna 
cerebri  is  pulled  upon  and  this  in  turn  pulls  in  a  caudad 
direction  the  tela  and  the  plexus,  and  gives  the  impression 
that  the  ventricle  is  not  entirely  covered  by  this  membrane 
as  shown  in  Plate  XIV;  this,  however,  is  not  the  case  as 
the  tela  covers  the  ventricle  completely. 

The  floor  of  the  ventricle  is  formed  by  those  structures 
found  in  the  locus  interpeduncularis ;  the  frontal  boundary 
consists  of  the  columnge  fornicis,  the  commissura  anterior, 
lamina  terminalis  and  the  caudal  extremity  of  the  septum 
peducidum. 

Examine  carefully  to  see  whether  the  cavity  of  the  ven- 
triculus tertius  extends  between  the  two  laminae  of  the 
septum  pellucidum. 

The  caudal  wall  is  formed  by  the  corpus  pineale,  the 
lamina  pinealis  and  the  cephalic  orifice  of  the  aquaeductus 
cerebri. 

The  lateral  walls  are  formed  on  either  side  by  the  thalami 
and  the  trigona  habenulge.  The  central  part  of  the  ven- 
tricle is  bridged  across  by  the  massa  intermedia,  and  at  the 
extreme  caudal  extremity  it  is  crossed  by  the  commissura 
posterior.  That  part  of  the  ventriculus  tertius  lying  cephal- 
ad  to  the  massa  intermedia  is  occasionally  called  the  aula. 
The  ventriculus  tertius  communicates  with  each  ventricu- 
lus lateralis  by  means  of  the  foramen  interventriculare,  and 
with  the  ventriculus  quartus  through  the  aquaeductus  cere- 
bri.    (Plate  XX.) 

There  is  a  hollow  projection  composed  of  substantia 
grisea  protruding  ventrad  from  the  floor  of  the  ventricle, 


AXATOMY    OF    THE    BRAIN  81 

the  infundibiilum.  This  structure  is  about  3  mm.  in 
length  and  2  mm.  in  diameter,  very  friable  and  invariably 
injured  when  any  effort  is  made  to  remove  the  hypophysis 
and  at  the  same  time  retain  its  connection  with  the  en- 
cephalon. 

The  hypophysis  (pituitary  body)  rests  in  the  fossa  hy- 
pophyscos  (sella  turcica),  and  when  the  structures  are  in 
their  normal  position  it  is  joined  to  the  encephalon  by 
means  of  the  infundibulum.  That  portion  of  the  infundib- 
ulum  which  remains  attached  to  the  encephalon  after  the 
removal  of  the  hypophysis  can  be  plainly  seen  on  the 
ventral  surface,  Plate  VII. 

Reflect  the  pia  mater  from  one  of  the  thalami  and  from 
the  ventral  surface  of  the  encephalon;  then  cut  off  one 
tractus  opticus  close  to  the  chiasma  opticum,  and  gradually 
tease  the  tractus  away  from  its  attachment  to  the  peduncu- 
lus  cerebri,  and  note  its  distribution  to  the  pulvinar,  col- 
liculus  superior  of  the  corpora  quadrigemina,  and  the  cor- 
pus geniculatum  externum. 


82  ANATOMY    OF   THE   BRAIN 


CHAPTER  XXII. 


THE  CORPORA  QUADRIGEMINA. 

The  corpora  quadrigemina  (Plates  VIII,  XV,  XXI, 
XXV  and  XXXVIII)  are  four  rounded  eminences  lying 
between  the  thalami  and  the  cerebellum. 

The  CoLLicuLi  SuPERioRES  (anterior  pair,  nates)  are  two 
quite  large  bodies,  hemispherical  in  shape  and  in  the 
sheep  much  greater  in  size  than  those  lying  directly  ventral 
called  the  colliculi  inf&riores  (posterior  pair,  testes.)' 

They  are  exposed  by  gently  separating  the  cerebrum 
from  the  cerebellum.  The  structure  of  the  colliculi  s\j 
periores  is  quite  complicated  and  difficult  to  demonstrate 
in  unstained  sections;  much  patience  will  therefore  be  re- 
quired for  their  dissection.  The  cortex  of  these  bodies  is 
about  1  mm.  in  thickness,  is  composed  largely  of  substantia 
grisea,  and  serves  for  the  termination  of  a  large  number 
of  the  fibres  of  the  tractus  opticus.  The  deep  portions  of 
these  colliculi  consist  mostly  of  transverse  fibres  that  pass 
between  the  colliculi,  forming  a  sharp  dip  ventrad  beneath 
the  sulcus  inter-collicularis  superior. 

In  sections  of  the  mesencephalon  of  the  sheep's  brain 
through  the  colliculus  superior  and  stained  by  the  Pal- 
Weigert  process  and  contrasted  with  Upson's  carmine,  four 
stratae  can  be  distinguished  with  the  naked  eye.  Accord- 
ing to  the  description  of  the  human  colliculus  superior, 
these  layers  would  be  called : 

1.  Stratum   zonale. 

2.  Stratum  cinereum. 

3.  Stratum  opticum. 

4.  Stratum  lemnisci. 

The  stratum  opticum  is  largely  composed  of  modulated 
fibres  from  the  tractus  opticus.  If  the  same  section  is 
studied  with  the  low  power  of  a  dissecting  microscope,  at 
least  six  distinct  layers  can  be  seen  lying  between  the 
surface  of  the  colliculus  and  the  central  grey  substance. 

Transverse  fibres  run  laterad  and  ventrad,  and  pass  be- 


ANATOMY    OF    THE    BRAIN  83 

Death  the  librse  poutis  superticialis  and  finally  caudad  to 
end  in  nuclei  situated  beneath  the  ventral  surface  of  the 
caudal  extremity  of  the  medulla  oblongata.  This  strand 
of  fibres  can  be  readily  teased  out  if  the  fibrje  pontis  super- 
ficiales  have  been  previously  removed.  The  colliculi  su- 
periores  are  separated  by  the  sulcus  inter-collicularis  supe- 
rior at  the  bottom  of  which  are  found  two  bundles  of 
white  fibres  running  in  the  direction  of  the  sulcus,  and 
dorsal  to  the  transverse  fibres  just  referred  to ;  these  sagit- 
tally  directed  fibres  will  be  discussed  when  considering  the 
remaining  colliculi. 

The  Colliculi  Inferiores  are  much  smaller  in  the 
sheep  than  the  colliculi  superiores  and  are  composed  almost 
wholly  of  substantia  alba.  Their  relations  are  very  peculiar 
and  interesting ;  to  each  colliculus  fibres  can  be  traced  from 
the  pars  centralis  thalami,  passing  caudad  through  the 
sulcus  inter-collicularis  superior,  around  the  caudal  border 
of  the  colliculus  superior,  where  they  join  the  substantia 
grisea  which  forms  the  colliculus  inferior.  From  the  lateral 
extremity  of  the  colliculus  inferior,  fibres  constituting  the 
hrachium  quadrigeminum  inferius  (Plate  XXIV)  can  be 
traced  cephalad,  resting  in  the  sulcus  between  the  dorsal 
border  of  the  pedunculus  cerebri  and  the  colliculus  su- 
perior; they  then  take  a  curved  dorso-caudad  direction  and 
help  to  form  the  caudal  portion  of  the  corona  radiata,  and 
eventually  are  distributed  to  the  substantia  grisea  of  the 
caudal  extremity  of  the  hemisphasrium. 

This  tract  can  be  clearly  seen  if  the  tractus  opticus  be 
cut  off  close  to  the  chiasma,  and  then  carefully  raised 
from  the  pedunculus  cerebri. 

In  .stained  sections  of  the  colliculi  inferiores,  the  nucleus 
of  each  can  be  clearly  seen  as  a  round  mass  of  matter, 
surrounded  by  medulated  nerve  fibres.  These  fibres  are 
derived  from  the  lemniscus  lateralis  of  both  sides  of  the 
mesencephalon.  Many  of  the  fibres  can  be  traced  dorsal 
to  the  colliculus  inferior  and  across  to  the  opposite  side. 

The  fibres  of  the  lemniscus  lateralis  from  the  floor  of 
the  trij.'-fiiuiii  Iciiinisci  }is  described  on  page  102  and  shown 
in  Plate  XXTT. 


84  ANATOMY   OF    THE   BRAIN 


CHAPTER  XXIII. 

CEREBRAL  PEDUNCLES. 

Leading  caudacl  and  ventrad  from  the  hemisphgeria  are 
the  pedmiculi  cerebri  (Plate  VII),  emerging  from  the  ven- 
tral surface  of  the  encephalon  between  the  lobi  hippocampi. 
These  pedunculi  converge  as  they  pass  caudad,  and  meet 
just  before  they  reach  the  cephalic  border  of  the  pons, 
where  they  disappear  beneath  the  fibraB  pontis  superficiales. 
On  their  ventral  surface  is  seen  the  caudal  portion  of  the 
circulus  arteriosus.  From  the  ventral  surface  of  each  pe- 
dunculus,  close  to  its  mesial  border  will  be  seen  arising  the 
N.  oculomotorius,  from  a  well  marked  groove  called  the 
sulcus  oculomotorius.  Winding  around  the  external  border 
from  the  dorsal  aspect,  comes  the  N.  trochlearis. 

The  N.  oculomotorius  in  most  animals  does  not  emerge 
from  its  sulcus  as  a  firm  round  solid  fasciculus,  as  one 
would  suppose  from  the  illustrations  shown  in  most  works 
on  human  and  comparative  anatomy,  but  is  formed  by  the 
union  o^  a  large  number  of  individual  fibres  similar  in 
manner  to  the  formation  of  the  N.  hypoglossus  as  de- 
scribed on  page  45. 

Passing  transversely  across  the  ventral  surface  of  the 
pedunculus  is  a  very  small  and  generally  indistinct  band 
of  nerve  matter  called  the  tractus  peduncularis  trans- 
versus.  This  tract  passes  laterad  about  3  mm.  cephalad  to 
the  superficial  origin  of  the  N.  oculomotorius,  until  it 
reaches  the  sulcus  between  the  corpus  geniculatum  internum 
and  the  colliculus  superior  and  thence  in  some  rare  eases 
can  be  apparently  traced  to  the  trigonum  habenulge  as  de- 
scribed in  a  subsequent  study  of  the  lateral  area  of  the 
medulla  oblongata. 

On  the  ventral  surface  of  the  pedunculus  near  its  mesial 
line  is  also  seen  a  conical  bundle  of  fibres  lying  in  a  direc- 
tion parallel  to  the  general  course  of  the  peduncle,  with 
its  apex  pointing  toward  the  pons.  This  mass  contains  the 
fibres  of  the   tractus  pyramidalis.  which,   traced   caudad, 


ANATOMY   OF    THE   BRAIN  85 

pass  dorsal  to  the  fibrae  poutis  superficiales,  and  emerge  at 
the  caudal  border  of  the  pons  as  the  pyramis  ventralis  as 
shown  in  Plates  XXIII,  XXX,  XXXV,  XXXVI, 
XXXVII.  Tracing  this  mass  cephalad  it  will  be  seen  to 
form  a  considerable  part  of  the  corona  radiata ;  this  corres- 
ponds to  the  genu,  and  the  cephalic  part  of  the  pars  postiea 
capsulge  internse,  on  its  way  to  the  cerebral  cortex. 

The  apparently  rapid  diminution  in  the  size  of  the 
tractus  pyramidalis  as  it  approaches  the  pons,  is  due  part- 
ly to  its  increased  thickness,  dorso-ventrally,  and  in  part 
to  the  large  number  of  its  fibres  and  collaterals  that  are 
distributed  to  the  motor  nuclei  of  the  Nn.  cerebrales. 

A  very  simple  procedure  will  show  the  formation  of  the 
corona  radiata  as  shown  in  Plate  XXII.  Take  the  side  of 
the  encephalon  from  which  the  tractus  opticus  has  been 
removed,  and  tear  away  the  lobus  hippocampi  with  that 
portion  of  the  cerebrum  lying  immediately  ventral  to  it. 

In  order  to  ascertain  the  direction  and  distribution  of 
such  fibres  as  those  constituting  in  part  the  pyramis  ven- 
tralis, pick  up  a  small  bundle  and  pull  or  tease  them  gently, 
and  they  will  be  lifted  from  their  course  very  distinctly. 

Make  an  incision  passing  transversely  through  the  crura 
at  the  level  of  the  exit  of  the  N.  oculomotorius,  which  in- 
cision also  passes  through  the  corpus  genieulatum  internum 
and  the  cephalic  portion  of  the  colliculus  superior,  and  note 
the  nucleus  ruber. 

No  tissue  resembling  the  substantia  nigra  of  the  pedun- 
euli  cerebri  of  the  human  encephalon  can  be  found  in 
the  peduncles  of  the  sheep's  brain.  In  contrasted  Pal- 
Weigert  sections,  groups  of  small  ill-defined  cells  can  be 
seen  ventro-laterad  to  the  nucleus  ruber,  where  the  sub- 
stantia nigra  would  be  looked  for,  but  no  pigment,  gran- 
ular or  otherwi.se,  could  be  discerned. 

There  are  some  large  cells  in  this  locality,  resembling 
those  found  in  the  nuflcus  ruber,  but  none  of  these  con- 
tained pigmctit. 

Consult  J'lates  XXIX,  XXXVIII,  ;ind  note  how  the 
constituent  elements  after-  they  emerge  from  its  nucleus, 
converge  to  form  the  N.  oculomotfti-ius  and  the  course  of  the 
nerve    fibrils    from    the   substantia   grisea    ventral    to    the 


86  ANATOMY    OF    THE   BRAIN 

aquaaductus  cerebri ;  also  that  on  its  way  to  the  mesial  sur- 
face of  the  crus  it  passes  through  a  large  collection  of  sub- 
stantia grisea,  the  nucleus  ruber. 

Note  the  aquseductus  cerebri  with  a  comparatively  thick 
wall  of  substantia  grisea,  and  that  the  aqugeduct  is  not 
circular.  Observe  also  that  the  transverse  band  of  sub- 
stantia alba  2  mm.  dorsal  to  the  aqueduct ;  this  band  is 
composed  of  the  transverse  fibres  of  the  colliculus  superior. 
On  the  lateral  border  of  this  section  (Plate  XXIX,  fig. 
1,  Plate  XXXyill)  will  be  noticed  a  slight  elevation, 
which  is  the  corpa  geniculatum  internum  and  externum, 
and  ventral  to  this  is  a  much  smaller  elevation,  very 
slight  in  some  instances,  representing  a  section  of  the 
tractus  peduncularis  transversus.  Dorsal  to  the  corpus 
geniculatum  externum  in  the  same  figure  is  another  quite 
small  projection,  a  section  of  the  brachium  quadrigeminum 
inferius. 

A  section  of  the  pedunculi,  intermediate  between  the 
exit  of  the  N.  oculomotorius  and  the  cephalic  extremity  of 
the  pons  is  very  nicely  shown  in  Plate  XXIX,  fig.  2,  illus- 
trating the  brachia  eonjunctivai  and  the  tractus  pyramidalis 
pedunculi  as  well  as  the  caudal  extremity  of  the  aquse- 
ductus cerebri  about  which  are  arranged  four  bundles  of 
longitudinal  fibres. 

Plate  XXIX,  fig.  3,  represents  a  section  immediately 
cephalad  to  the  pons  showing  the  cephalic  extremity  of 
the  ventriculus  quartus  and  the  various  structures  enumer- 
ated in  the  preceding  section. 

These  sections  are  very  helpful  in  making  clear  the  rela- 
tions of  these  various  tracts,  as  well  as  showing  clearly  the 
composite  nature  of  the  crura  cerebri.  These  sections 
should  be  carefully  studied  and  drawings  made.  Coronal 
or  transverse  sections  will  be  found  to  assist  the  student 
greatly  in  understanding  the  dissections  showing  the  vari- 
ous strands  and  tracts. 

Students  should  be  given  stained  sections,  through  the 
nucleus  ruber,  showing  the  nucleus  and  efferent  fibres  of 
the  N.  oculomotorius.  These  should  be  studied  and  com- 
pared with  the  gross  preparation,  as  shown  in  Plate 
XXXVIII. 


ANATOMV    OK    TlIK    BRAIN  87 


CHAPTEU  XXIV. 


jPt 


THE  PONS. 

The  pons  (pons  Varolii,  cerebellar  bridge),  Plates  XXIII, 
XXIV,  and  XXV,  is  a  large  band  of  substantia  alba,  lying 
in  a  coronal  plane  of  the  eneephalon.  Its  greatest  longi- 
tudinal diameter,  is  a  little  to  each  side  of  the  median  line 
where  it  will  average  about  1  cm.;  at  its  extremities,  just 
as  it  is  about  to  enter  the  cerebellar  hemispheres  it  will 
measure  about  8  mm.  The  central  portion  of  the  pons  is 
marked  by  a  well  developed  sulcus  hasilaris  in  which  rests 
the  A.  basilaris. 

At  the  caudal  extremity  of  this  sulcus  Avill  be  observed 
a  small  triangular  depression,  with  its  apex  cephalad  oc- 
cupied by  the  Aa.  eerebelli  posteriores.  The  prominent 
convexities  on  either  side  of  the  sulcus  basilaris  mark  the 
location  of  the  pontal  nuclei  and  the  tibres  of  the  tracti 
pyramidales.  As  the  pyramidal  tracts  pass  through  the 
pons  they  are  called  the  fasciculi  longitudinales  super- 
ficiales  pontis  (pyramidales).  and  can  be  plainly  seen  by 
making  an  incision  in  the  course  of  the  sulcus  basilaris 
and  reflecting  the  fibrae  pontis  superficialis ;  sections  of 
these  fibra^  are  shown  in  Plate  XXX,  fig.  1.  This  dissection, 
however,  should  be  deferred  until  the  ventral  and  lateral 
surfaces  of  the  medulla  oblongata  have  been  studied.  It 
will,  of  course,  be  noted  that  the  caudal  margin  of  the 
pons  is  quite  straight  while  the  convexity  of  the  cephalic 
margin  is  veiy  marked. 

As  the  pons  passes  laterad  on  either  side  it  takes  a  sharp 
turn  dorsad  and  passes  directly  to  the  hemisphaeria  eere- 
belli forming  the  hrachia  pontis  (the  middle  cerebellar 
peduncles).  Rising  from  the  lateral  portions  of  the  pons 
are  the  Nn.  trigemini  which  are  situated  near  the  caudal 
margin ;  if  the  nerve  be  pressed  caudad  the  fibres  can  be 
plainly  seen  passing  between  the  various  strands  of  the 
fibrae  pontis  superficiales. 

Examine  the  nerve  clo.sely  and  it  will  be  seen  to  consist 
of  two  bundles;  that  placed  laterad  is  sensory  and  much 


88  ANATOMY    01''    THE   BRAIN 

larger  than  the  smaller  or  motor  fasciculus  placed  mediad. 
The  further  dissection  of  this  nerve  will  be  undertaken  at 
a  later  stage. 

Just  dorsad  to  the  N.  trigeminus  is  a  well  developed  and 
distinct  mass  of  cerebellar  tissue,  the  flocculus  (Plate 
XXIII). 

If  a  specimen  be  prepared  by  the  Kaiserling  method  it 
Avill  be  well  to  make  some  sections  through  the  entire  sub- 
stance of  the  pons  parallel  with  the  transverse  fibres. 

This  dissection  will  show  quite  plainly  a  deep  set  of 
transverse  fibres  the  fibrae  pontis  profmidae  (Plate  XXX, 
fig.  1)  about  4  mm.  from  the  ventral  surface.  These 
transverse  fibres  are  quite  white  in  color  and  readily  dis- 
tinguishable from  the  longitudinal  fibres  that  have  the  ap- 
pearance of  substantia  grisea.  The  fibrge  pontis  pro- 
fundge  must  not  be  mistaken  for  the  deep  transverse  fibres 
so  often  mentioned  as  the  trapeziums  in  works  on  human 
anatomy.  In  Weigert-staiu^d  sections  of  the  sheep's  brain 
the  fibrae  pontis  profundae  jan  be  clearly  traced  to  the 
brachia  pontis. 

Besides  these  two  groups  there  exist  a  ^"^itral  group 
of  longitudinal  fibres,  the  fasciculi  lon^^i^  jdintu^venL'^upGi'- 
ficiales  pontis  previously  mentioned;  and  the  fascicu\  ongi- 
tudinaies  profundis  pontis  that  occupy  a  minor  poicio^  of 
the  dorsal  two-thirds  of  the  pons.  This  fasciculus  is  ai.  ^t 
2  mm.  ventrad  to  the  surface  of  the  eminentia  mediaiis 
and  close  to  the  mesial  line ;  it  is  often  called  the  fasciculus 
longitudi^ialis  mediaiis;  this  fasciculus  is  very  distinctly 
seen  when  the  section  is  held  up  to  the  light. 

If  the  sectioning  be  made  through  the  cephalic  margin 
of  the  pons,  the  hrachia  conjunctiva  (superior  cerebellar 
peduncles)  are  very  plainly  seen  as  two  pronounced  folds 
of  substantia  alba  at  the  dorso-lateral  borders  (Plate  XXX, 
fig.  1). 

In  the  midline  will  also  be  seen  a  distinct  septum  divid- 
ing the  white  matter  of  the  pons  into  two  symmetrical 
halves ;  this  septum  is  called  the  raphe  pontis.  The  dorsal 
concave  surface  of  the  pons  forms  part  of  the  cephalic 
half  of  the  floor  of  the  ventriculus  quartus,  and  the  sharp 


ANATOMY   OF    THE   BRAIN  89 

dip  111  the  centre  of  this  surface  is  the  sulcus  longitudiualis 
fo«sae  rhomboideic,  the  elevation  laterad  to  this  sulcus  is 
the  eminentia  luedialis;  these  structures  will  ]ye  further 
considered  in  the  study  of  the  ventriculus  quartus  (see 
Plate  XXX,  fig.  2). 

If  another  transverse  incision  be  made  at  the  level  of 
the  exit  of  the  N.  trigeminus  the  two  transverse  fibrous 
masses  will  be  seen  to  unite  on  either  side  and  form  the 
brachium  pontis. 

In  sections  of  this  region  of  the  encephalon,  the  large 
area  dorsal  to  the  fibras  pontis,  has  a  very  irregular  con- 
struction, and  to  the  naked  eye,  appears  to  be  perfectly 
homogeneous,  except  for  the  fasciculi  longitudiualis  pro- 
f undis  pontis.  This  area  is  the  formatio  reticularis ;  a  most 
beautiful  picture  in  the  stained  section,  and  a  fascinating 
hunting  ground  for  the  neurologist. 

In  this  connection  students  should  be  given  stained  trans- 
verse sections  of  the  pons,  to  ?piDress  upoii  them  a  right 
idea  of  the  wide  distribution  ^f  tne  nuclei  pontis.  These 
nuclei  are  very  exte^isive  and  have  always  been  inade- 
quately illuvtrated  and  described  in  works  on  human  and 
compPxC  t9-e  an'Jt-^iny. 
If 


'V 


90  ANATOMY    OF    THE   BRAIN 


CHAPTER  XXV. 


THE  TRAPEZIUM. 

The  trapezium  (Plates  XXIII,  XXX,  fig.  3,  and  Plate 
XXXVII)  is  a  transverse  band  of  fibres,  the  borders  of 
which  are  nearly  parallel.  It  occupies  the  space  between 
the  medulla  oblongata  and  the  pons.  Its  Madth  is  nearly 
4  mm.  and  it  extends  completely  across  this  portion  of  the 
encephalon. 

About  midway  between  its  borders  and  3  mm.  from  the 
middle  line  will  be  seen  the  exit  of  the  N.  abducens  (sixth 
pair).  At  its  lateral  extremities  are  two  large  nerves,  the 
N.  facialis  and  the  N.  acusticus.  The  N.  facialis  (seventh 
pair,  portio  dura  of  Willis)  is  easily  identified  and  arises 
superficially,  from  the  cephalic  half  of  the  lateral  portion 
of  the  trapezium.  Its  appearance  is  distinctly  fibrillar  and 
it  passes  laterad  in  a  plane  parallel  with  the  ventral  sur- 
face of  the  trapezium  after  its  exit ;  the  nerve  can  be  readily 
dissected  centrally  toAvard  its  genu  (knee)  which  forms 
the  eminentia  facialis  situated  in  the  floor  of  theVentricuIus 
quartus,  if  the  tissue  be  carefully  cleared  away  from  the 
lateral  side  of  the  nerve.  Or,  still  better,  make  an  incision 
through  the  centre  of  the  trapezium  parallel  with  its  long 
diameter  or  parallel  to  the  caudad  border  of  the  brac^hium 
pontis,  thus  making  a  section  as  shown  in  Plate  XXX,  fig. 
3,  and  the  course  of  the  nerve  can  be  very  distinctly  seen. 

If  the  section  be  fortunately  made  along  the  caudal  bor- 
der of  the  nerve,  it  can  be  elevated  from  the  surrounding 
tissue  and  traced  directly  to  the  genu.  In  the  same  section 
will  be  shown  some  fibres  of  the  N.  abducens  passing  ven- 
trad  a  few  mm.  from  the  middle  line.  This  section  also 
clearly  illustrates  the  large  portion  of  the  ventriculus 
quartus  that  is  occupied  by  the  vermis  cerebelli  minor, 
as  well  as  showing  the  radix  ascendens,  N.  trigemini 
(tractus  spinalis  N.  trigemini)  and  the  corpus  restiforme; 
the  two  latter  lying  laterad  to  the  N.  facialis. 

The  N.  acusticus   (eighth  pair,  portio  mollis  of  Willis) 


AXAT():\IY    OF    THE    BRAIX  91 

is  seen  immGcliately  caudad  to  the  N.  facialis  and  it  can 
be  traced  from  the  tnberciilnm  aeusticnm  in  the  recessus 
lateralis  ventriciili  quarti,  around  the  corpus  restiforme  ly- 
ing ventrad  to  the  floeciihis.  This  nerve  is  very  soft  and 
easily  torn  so  that  considerable  care  must  be  taken  in  its 
study  or  it  will  be  spoiled  and  the  usefulness  of  the  dis- 
section destroyed.  The  course  of  the  N.  aciLsticus  as  it 
winds  around  the  corpus  restiforme  is  clearly  displayed  in 
Plates  XXIII.  XXIV  and  XXV.  An  elevation!  well 
marked  in  most  specimens,  is  seen  on  each  side  of  the 
middle  line  of  the  trapezium ;  this  is  caused  by  the  pyramis 
medulla^  oblongata?  at  the  pyramis  pa.sses  caudad,  ventrad 
to  the  fibres  constituting  the  trapezium,  to  reach  the 
medulla  oblongata. 

Sections  through  the  trapeziurti,  cut  in  the  direction  of 
the  long  diameter  of  the  nucleus  dorsalis  N.  coclilearis  {N. 
acusticus)  and  stained  by  Pal-Weigert  process  should  be 
supplied  to  the  student  for  study  and  drawing.  (See 
Plate  XXXVII.) 

Fibres  of  the  N.  coclilearis  should  be  traced  to  the  nu- 
cleus dorsalis  N.  cochlearis,  and  from  this  nucleus  other 
fibres  are  to  be  traced  into  the  area  acustica  of  the  fourth 
ventricle,  and  on  toward  the  sulcus  longitudinalis  fossae 
rhomboideje  as  the  stricc  medullares  (stricc  acusticece) . 

Another  fasciculus  from  the  X^.  coclilearis  can  be  traced 
into  the  nucleus  ventralis  N.  cochlearis,  which  lies  just 
ventrad  to  the  corpus  restiforme  and  from  which  latter 
nucleus,  fibres  can  be  seen  entering  the  corresponding  ex- 
tremity of  the  trapezium. 

The  A'',  vestibularis  (N.  acusticus)  is  distinctly  seen 
passing  in  a  dorso-mesial  direction,  through  the  substance 
of  the  brain-stem,  toward  the  nucleus  N.  vestibularis  which 
lies  toward  the  floor  of  the  fourth  ventricle.  This  nucleus 
is  sometimes  called  the  "principal  vestibular  nucleus''  or 
the  nucleus  dorsalis  N.  vestibula/ris. 

Just  mediad  to  the  dorsal  vestibular  nucleus  is  the  I'adix 
df'seendens  N.  vestibularia.  Scattered  amidst  these  descend- 
ing fibres  are  large  multipolar  cells,  easily  seen  with  the 
dissecting   microscope    in    contrasted    sections.      Those    of 


92  ANATOMY    OF    THE   BRAIN 

these  cells  that  lie  caudacl  in  the  radix  descendens  N.  ves- 
tibularis, constitute  what  is  called  Deiter's  nucleus,  while 
those  that  are  located  in  the  caudal  portion  of  the  radix 
for  the  nucleus  of  Bechterew. 

In  each  lateral  half  of  the  trapezium,  5  mm.  from  the 
raphe  and  quite  close  to  the  ventral  surface,  is  a  circular 
light  area  about  1  mm.  in  diameter,  the  nucleus  olivaB  in- 
ferior; see  Plate  XXX,  XXXI  and  XXXVII.  Immedi- 
ately laterad  to  the  olive  nucleus  is  another  light  area,  of 
slightly  larger  dimensions,  containing  large  multipolar 
cells,  seen  in  contrasted  sections  with  the  dissecting 
microscope,  constituting  the  nucleus  facialis.  A  wide 
spray  of  fibres  visible  to  the  naked  eye  in  Pal-Wei- 
gert  sections  can  be  seen  converging  toward  the  emi- 
nentia  facialis  on  the  floor  of  the  fourth  ventricle, 
close  to  the  sulcus  longitudinalis.  These  fibres  form 
the  pars  prima  N.  facialis  (radicular  part),  and  as 
they  reach  the  floor  of  the  ventricle  just  dorsad  to  the 
nucleus  N.  ahducentis  (Pi  te  XXXVII),  they  assume  a 
fascicular  form.  This  fasciculus  then  passes  cephalad  for 
a  short  distance,  lying  mediad  to  u.  i  nucleus  of  the  abdu- 
cens  nerve  forming  the  genu  N.  facialis  (ascending  part). 
The  nerve  then  turns  sharply  ventro-laterad  to  reach  the 
surface ;  this  is  the  pars  secunda  N.  facialis  or  emerging 
part  (fig.  3,  Plate  XXX). 


ANATOMY    OP    THE    BRAIN  93 


CHAI'IER  XXVI. 

STRUCTURE  OF  THE  MEDULLA  OBLONGATA. 
VENTRAL  SURFACE. 

The  medulla  oblongata  {medulla,  marrow;  ohlongus, 
greater  in  length  than  in  bi-eadth;  cerebral  protuberance 
of  Goll).  The  lower  extremity  is  called  the  "tail  or  rachi- 
dian  bulb;"  bulbns  medullae  spinalis  seu  rachidicus; 
French,  bulbe  rachidian— Dunglison;  see  Plates  XXIII, 
XXIV  and  XXV. 

In  order  to  obtain  the  best  results  from  a  microscopic 
examination  of  the  encephalon,  the  specimen  should  be 
hardened  in  a  large  quantity  of  a  ten  per  cent  solution 
of  formalin  for  at  least  a  month.  Take  the  specimen  from 
the  formalin  solution  and  place  it  in  water  for  a  week  or 
two,  changing  the  water  several  times;  the  preparation 
will  then  be  in  the  best  possiV'^  condition  for  inspection. 
In  fact,  the  longer  the  material  remains  in  the  hardening 
solution  the  better.  It  ..as  oeen  found  that  medullae  pre- 
pared by  tnis  simple  method  present  the  superficial  mark- 
ings much  more  distinctly  than  when  they  are  examined 
immediately  after  removal  from  the  skull  or  after  a  shorter 
imme.'jion  in  formalin.  The  myelin  sheaths  of  the  nerve 
fibres  swell  from  the  absorption  of  Avater,  while  the  con- 
nective tissue  which  is  apparently  in  greater  quantity  be- 
tween the  various  fasciculi,  does  not.  This  in  all  probabil- 
ity, explains  the  prominence  assumed  by  the  various  tracts, 
after  immersion  in  water,  that  previously  were  very  in- 
distinct or  absolutely  invisible  to  the  naked  eye. 

The  student  will  find  several  tracts  located  in  the  me- 
dulla oblongata  very  difficult  to  identify  unless  some  care 
is  exercised  in  preparing  the  specimen,  but  with  applica- 
tion, and  a  good  specimen  the  tracts  to  be  enumerated  can 
be  found  and  named. 

That  portion  of  the  encephalon  under  consideration  is 
perhaps  the  most  difficult  of  any  of  the  subdivisions  of  the 
central    nervous   system    to    analyze,    and    nothing   is   at- 


94  ANATOMY   OF   THE   BRAIN 

tempted  in  the  present  connection  except  the  superficial 
markings,  and  those  structures  that  are  apparent  in  the 
ventriculus  quartus.  The  nuclei  of  origin  of  the  nei-vi 
cerebrales,  the  central  nuclei,  and  the  deep  lying  tracts, 
will  not  be  now  considered  to  any  great  extent. 

It  is  of  great  assistance,  however,  to  the  student  in  medi- 
cine, while  studying  the  medulla  oblongata,  to  have  several 
Pal-Weigert  sections  at  hand  as  when  studying  the  me- 
sencephalon, pons  and  trapezium.  In  these  stained  sec- 
tions many  important  structures  can  be  identified  with- 
out the  aid,  even  of  a  hand  glass,  viz. :  N.  hypoglossus, 
nucleus  N.  hypoglossus,  nucleus  olivae,  N.  vagus,  nucleus 
N.  vagi,  nucleus  tractus  spinalis  N.  trigemini,  traetus  soli- 
tarius,  nuclei  arcuati,  substantia  reticularis  alba,  substan- 
tia reticularis  grisea  &c. 

Sections  to  be  studied  in  this  manner  should  be  about 
30  to  40  microns  thick,  thoroughly  differentiated  and  not 
counterstained.  If  the  structure  of  the  various  nuclei 
is  to  be  studied  the  contrasted  sections  should  be  supplied 
as  well.     See  Plates  XXXIV,  XXXV  and  XXXVI. 

The  medulla  oblongata  measures  21  mm.  in  width,  17 
mm.  in  length  and  23  mm.  in  thickness;  those  measure- 
ments will  vary  to  a  limited  extent,  but  they  are  the  aver- 
age dimensions  computed  after  the  examination  of  about 
fifty  medullae. 

Before  removing  the  pia,  some  attention  must  be  de- 
voted to  the  consideration  of  the  arrangement  of  this  mem- 
brane near  the  caudal  extremity  of  the  vermis  cerebelli 
and  the  cephalic  portion  of  the  medulla  oblongata  in  the 
region  of  the  flocculus.  Look  for  the  aperaturae  ventric- 
uli  quarti  (foramen  of  Magendie),  and  examine  the  plexus 
chorioideus  ventriculi  quarti  on  either  side,  and  note  the 
close  relation  that  these  plexuses  bear  to  the  nervi  acustici, 
and  how  they  appear  to  follow  the  nerves  ventrad.  (Figs. 
D  and  E.) 

"When  separating  the  cerebellum  from  the  rest  of  the 
encephalon,  care  must  be  taken,  not  to  injure  the  valve  of 
Vieussens.  If  the  valve  be  closely  examined,  a  thick  trans- 
verse band  about  1  mm.  broad  can  be  seen  within  1  mm. 


ANATOMY   OF    THE    BRAIN  95 

of  its  cephalic  extremity.  This  is  the  decussation  of  the 
Nn.  troehleares.  Grasp  one  of  these  nerves  with  the  for- 
ceps and  gently  pull ;  it  can  be  traced  onto  the  margin 
of  the  valve  without  much  difficulty.  The  fibres  of  these 
ner\'es,  as  they  decussate,  form  an  interlocking  plait  in 
the  substance  of  the  valve  so  that  it  is  impossible  to  trace 
the  nerves  for  any  distance  in  the  substance  of  the  valve. 

The  tela  chorioidca  ventriculi  quarti  deserves  more  than 
a  passing  notice  at  this  time.  If  a  specimen  is  examined 
after  it  has  been  in  vs'ater  for  a  short  time,  and  before  any 
dissection  has  been  attempted  or  before  it  has  been  handled 
to  any  extent,  a  clear  idea  of  the  attachments  of 
the  tela  can  be  ascertained. 

Examine  the  angle  formed  by  the  caudal  surface  of 
the  vermis  cerebelli  and  the  dorsal  surface  of  the  medul- 
la oblongata.  Slightly  depress  the  medulla  oblongata  and 
a  comparatively  dense  miembrane  comes  into  view.  This 
is  a  portion  of  the  arachnoid,  and  is  reflected  from  the 
caudal  surface  of  the  vermis  and  hemispheria  cerebelli  to 
the  dorsal  surface  of  the  medulla  oblongata  where  it  is,  in 
some  specimens  very  firmly  attached,  as  indicated  by  the 
large  curved  red  line  in  fig.  E,  page  107.  In  the  neighbor- 
hood of  the  flocculus  this  part  of  the  arachnoid  becomes 
adherent  to  the  pia.  The  tela,  an  altogether  different 
structure,  is  not  at  all  effected  by  the  foregoing  manipula- 
tion, and  cannot  be  studied  until  the  caudal  part  of  the 
vermis  at  least,  has  been  removed,  when  it  can  be  seen 
sagging  down  into  the  cavity  of  the  ventricle.  It  forms 
the  roof  of  the  caudal  portion  of  that  cavity,  is  firmly 
attached  to  its  walls,  and  extends  cephalad  as  far  as,  and 
into  the  fissure  separating  the  vermis  major  from  the 
caudal  extremity  of  the  vermis  minor. 

The  attachments  of  the  tela  to  the  walls  of  the  ventricle 
are  shown  by  the  smaller  curved  red  line  in  fig.  E.  In  the 
immediate  neighborhood  of  the  ventricular  wall  it  is  very 
much  thickened  as  shown  in  transverse  section  in  Plates 
XXXV  and  XXXVI.  This  thickened  portion  of  the  tela 
is  called  the  lifjnla. 

The  plexus  of  the  tela  skirts  its  cephalic  border,  and  is 


96  ANATOMY   OF   THE   BRAIN 

particularly  abundant  in  each  extremity  of  this  border, 
close  to  the  flocculus;  completely  filling  in  the  angle  formed 
by  the  hemispheriuni  eerebelli^  the  flocculus  and  the  cor- 
pus restiforme.  The  red  convoluted  line  in  fig.  E  shows 
this  arrangement,  A  process  of  this  same  plexus  passes 
caudad,  attached  to  the  ventral  surface  of  the  tela  ven- 
trieuli  quarti,  hanging  suspended  in  the  cavity  of  the 
ventricle  as  seen  in  section  in  Plate  XXXVI. 

In  the  region  where  the  tela  is  attached  to  the  rami  obicis 
as  they  form  the  lateral  wall  of  the  caudal  third  of  the 
ventricle,  they  spread  out  into  broad  oval  masses  in  sec- 
tion, so  closely  attached  tq  the  eminentia  vagi  (ala  cinerea) 
that  they  are  distinguishable  only  when  stained.  This  par- 
ticular arrangement  will  be  further  considered  in  a  sub- 
sequent chapter. 

Now  remove  the  pia  completely  from  the  medulla  ob- 
longata, and  in  so  doing  the  nerves  will  be  detached,  but 
as  they  have  already  been  studied  this  will  do  no  harm. 
In  this  procedure  be  very 'careful  not  to  injure  the  delicate 
tissues  that  lie  in  the  vicinity  of  the  ventriculus  quartus. 

As  already  described  the  pia  begins  to  thicken  into  a  de- 
cidedly tough  and  fibrous  sheath  as  it  is  tra>  ed  toward  the 
caudal  extremity  of  the  medulla  oblongata,  anc  iheres 
very  tenaciously  to  the  tissues  inclosed.  It  is  specially 
difficult  to  remove  it  from  the  fissura  mediana  ventr^lis  of 
the  medulla  spinalis,  where  this  structure  joins  the  medulla 
oblongata. 

Make  an  incision  through  the  pia,  parallel  with,  and  on 
each  side  of  the  fissura  mediana  ventralis,  extending  to  the 
caudal  extremity  of  the  specimen,  and  gradually  detach 
the  membrane  towards  the  dorsal  surface ;  lastly  pull  away 
the  part  left  in  the  fissura  ventralis.  If  this  operation  be 
carefully  done,  none  of  the  delicate  lines  separating  the 
fasciculi  on  the  surfaces  of  the  medulla  oblongata  and  the 
medulla  spinalis  will  be  obliterated. 

In  Plate  XXIII  the  pia  is  enlarged  out  of  proportion, 
and  a  diagramatie  space  shown  between  the  cord  and  pia, 
that  does  not  exist  in  nature. 

In  the  median  line  of  the  ventral  surface  is  seen  the 


ANATOMY   OF    THE    BRAIN  97 

fissitra  media na  ventralis,  extending  from  tlie  caudal  ex- 
tremity of  the  sulcus  basilaris  to  the  cephalic  ending  of 
the  fissura  mediana  ventralis  medullae  spinalis. 

This  so-called  fissure  of  the  medulla  oblongata  is  really 
not  a  fissure,  but  a  sulcus,  the  fissure  having  been  obliterat- 
ed by  the  decussation  of  the  fibres  of  the  pyramides  medul- 
lae oblongatae  passing  from  one  side  of  the  medulla  to  the 
other;  clearly  shown  in  Plate  XXXIV. 

On  examining  the  medullae  of  nearly  a  hundred  en- 
cephala,  it  was  impossible  to  find  any  large  bundles  of 
fibres  passing  from  one.  side  of  the  medulla  to  the  opposite 
side  of  the  cord,  a  condition  contrary  to  what  we  find  in 
the  human  brain,  where  the  decussating  bundles  are  so 
clearly  seen  by  the  naked  eye. 

On  either  side  of  the  sulcus  ventralis  is  a  well  marked 
band  of  tissue  called  the  pyramis  (the  anterior  or  ventral 
pyramids)  which  is  separated  from  the  remaining  portion 
of  the  lateral  half  of  the  medulla  oblongata  by  the  sulcus 
ventralis  lateralis  (antero-later^l  fissure)  ;  this  sulcus  is 
very  distinct  ceyjhalad,  but  becomes  very  indistinct  as  it 
is  traced  caudad. 

The  p"'"^  im  Is  ar.  at  their  greatest  width  as  they  lie  in 
the  c  al  part  of  the  medulla,  but  as  they  are  traced 
cephalaa  they  become  gradually  narrower  and  more  dis- 
tinct j  each  tract  appears  to  break  up  into  strands  of  fibres. 
The  median  bundles  reach  the  caudal  border  of  the  pons, 
superficial  to  the  trapezium,  Avhile  the  lateral  bundles  pass 
dorsad  to  the  superficial  fibres  of  the  trapezium  prior  to 
reaching  the  pons,  constituting  the  fasciculus  longitudina- 
lis  superficialis  pontis  (see  Plate  XXX),  where  transverse 
sections  of  these  bundles  of  fibres  are  nicely  shown.  By 
reflecting  the  fibrae  pontis  superficialis  the  longitudinal 
course  of  the  fibrae  pyramidales  can  be  clearly  demon- 
strated by  tearing  the  fibrae  in  the  direction  in  which  they 
run.  Traced  caudad,  the  fibres  of  the  pyramis  take  a 
dorsal  direction  skirting  the  walls  of  the  fissura  ventralis. 
As  these  fibres  reach  the  bottom  of  the  fissure  they  turn 
abruptly  toward  the  opposite  si(l<\  cuttJTig  across  the  base 
of  the  colum;na  ventralis  to  reach  the  j)roc('ssiis  reticularis 


98  ANATOMY    OF    THE    BRAIN 

and  the  region  of  the  fasciculi  longitudinales  dorsales  as 
outlined  in  Plate  XXXIV.  These  decussating  fibres  are 
sometimes  collected  into  comparatively  large  fasciculi  or 
loose  bundles,  that  can  be  seen  with  the  low  power  of  the 
dissecting  microscope  even  in  unstained  sections.  These 
decussating  bundles  are  nothing  in  size  compared  to  the 
huge  bunches  that  cross  in  the  human  medulla  oblongata. 

Sections  that  are  cut  .5  mm.  in  thickness,  when  placed 
on  the  glass  stage  of  the  dissecting  microscope  over  the 
black  diaphragm  and  flooded  with  water,  show  these  de- 
cussating fasciculi  plainly.  Or  a  better  way  is  to  place 
the  freshly  cut  sections  on  dark  blue  glass  resting  on  white 
paper  and  flooding  with  water.  Now  by  using  a  focusing 
lense  to  illuminate  the  sections  the  medullated  fibres  be- 
come quite  brilliant,  and  even  very  small  fasciculi  becomie 
visible. 

Immediately  laterad  to  the  cephalic  third  of  the  pyramis 
can  be  found  a  very  delicate  and  sometimes  indistinct  strip 
of  white  substance,  here  called  the  fasciculus  lateralis 
miliar.  The  cephalic  extremity  of  this  tract  is  first  ob- 
served as  it  apparently  emerges  from  the  sulcus  separating 
the  pons  from  the  trapezium;  look  for  it  just  mediad  to 
the  exit  of  the  nervus  facialis  from  the  trapezium.  Occa- 
sionally considerable  persistence  must  be  exercised  to  iden- 
tify it,  but  a  careful  search  will  invariably  be  rewarded. 
Traced  eaudo-niediad  to  the  caudal  border  of  the  trape- 
zium, it  is  seen  to  approach  the  lateral  margin  of  the  py- 
ramis from  which  it  is  separated  by  a  distinct  depression, 
the  cephalic  extremity  of  the  sulcus  ventralis  lateralis. 
Traced  caudad  it  runs  for  a  short  distance  nearly  parallel 
with  the  fissura  mediana  ventralis;  it  then  takes  a  gradual 
bend  laterad  to  reach  the  lateral  aspect  of  the  medulla 
spinalis.  In  passing  obliquely  across  the  medulla  oblon- 
gata it  lies  laterad  to  the  exit  of  the  fibres  which  unite  to 
form  the  nervus  hypogiossus.  As  the  fasciculus  reaches 
the  miedulla  spinalis  it  becomes  quite  distinct  and  easily 
distinguishable  from  the  adjacent  tissues;  it  can  be  finally 
traced  to  the  superficial  area  of  the  medulla  spinalis,  about 


ANATOilY    OF    THE    BRAIN  99 

the  centre  ot  the  funieiihis  lateralis  as  shown  in  Plate 
XXXIIl. 

There  can  scarcely  be  any  question,  but  that  the  fasci- 
culus lateralis  minor  is  the  homologue  of  the  fasciculus 
ventrolateralis  superficialis,  commonly  called  Gower's  tract 
in  the  human  medulla  spinalis.  Authorities  on  human 
anatomy  place  this  fasciculus  jiLst  ventrad  to  the  centre 
of  the  funiculus  lateralis  on  or  near  the  surface ;  but  when 
it  reaches  the  medulla  oblongata,  they  bury  it  somewhere 
in  the  recticulai  formation  of  the  medulla  and  pons  on  its 
way  to  reach  the  brachium  conjunctivum,  in  the  substance 
of  which  it  passes  to  the  vermis  cerebelli.  In  the  encepha- 
lou  of  the  sheep  it  can  be  traced  to  the  trapezium  over 
which  it  passes,  directing  its  course  the  cerebellum.  In 
Pal-Weigert  sections  it  can  be  seen  as  a  compact  bundle  of 
fibres  on  the  ventral  surface  just  mediad  to  the  region  of 
the  nucleus  olivae.  See  Plates  XXXV,  XXXVI,  and 
XXXVII. 

Another  very  interesting  feature  of  the  medulla  oblon- 
gata is  the  oliva,  so  conspicuous  in  the  human  encephalon. 
Lying  one  on  each  side,  the  olivae  are  to  be  seen  immedi- 
ately caudad  to  the  trapezium,  resting  in  the  obtuse  angle 
formed  by  the  caudal  border  of  the  trapezium  and  the 
lateral  border  of  the  fasciculus  lateralis  minor.  The  olivae 
are  very  indistinct  in  some  specimens,  but  in  others  again 
they  are  easily  seen,  and  their  superficial  relations  clearly 
evident. 

In  a  transverse  section  of  the  medulla  oblongata  passing 
through  the  olivae,  a  distinct  round  nucleus  can  be  seen 
close  to  the  surface  of  the  structure,  Plate  XXX.  fig.  3, 
and  Plate  XXXT.  fig.  1.  also  Plate  XXXVT. 

Laterad  to  the  olivae  on  each  side  will  be  seen  a  longi- 
tudinal tract  of  considerable  size  traceable  in  some  instances 
to  the  caudal  extremity  of  the  medulla  oblongata.  This 
lartre  bundle  is  the  trarhts  spinalis  N.  triiicmini  {radix 
asrrndens  N.  trif/rwini)  of  the  medulla  o])longata  and 
by  reflecting  the  superficial  transverse  fibres  of  the 
li-apczin'ii.  and   Ihf  adjoining  fibres  of  tlie  pons,  and  then 


100  ANATOMY    OF    THE    BRAIN 

teasing  the  nerve  caudad,  the  fibres  of  this  radix  can  be 
traced  nicely.  This  radix  rapidly  diminishes  as  it  is 
traced  caadad,  and  toward  its  termination  the  superficial 
boundaries  become  very  indistinct  if  not  quite  obliterated. 

As  the  pia  is  carefully  removed  from  this  eminence  a 
number  of  the  radices  forming  the  Nn.  glossopharyngeus 
et  vagus  will  be  seen  passing  from  the  medulla  between 
the  fibres  constituting  the  tractus  spinalis  N.  trigemini ; 
the  direction  of  the  line  of  exit  of  these  root  fibres  is  caudo- 
laterad,  and  they  appear  to  be  in  line  with  those  bundles 
of  fibres  that  constitute  the  radix  cerebralis  N.  accessorii. 

Another  feature  of  interest  is  the  presence  of  a  large 
number  of  arching  fibres  that  appear  to  emerge  from  the 
deep  tissue  of  the  medulla  oblongata  by  way  of  the  sulcus 
ventralis  lateralis.  They  are  found  on  the  cephalic  half  of 
the  medulla,  covering  the  caudal  part  of  the  oliva;  they 
pass  caudo-laterad  then  gracefully  change  their  course  to 
cephalo-dorsad  and  are  lost  on  the  surface  of  the  corpus 
restiforme  (Plate  XXIII,  Plate  XXXV). 

These  fibres  no  doubt  are  the  fihrae  arcvatae  externae, 
and  in  all  probability  are  analogous  to  the  striations  found 
in  the  corresponding  location  on  the  human  encephalon. 
These  fibrae  are  somewhat  difficult  to  find  in  some  speci- 
mens, but  they  are  there  and  a  determined  search  will  in- 
variably reveal  them.  In  other  encephala,  large  numbers 
of  these  fibres  reach  the  surface  and  cover  a  large  area 
of  the  ventral  and  lateral  surfaces,  extending  in  some 
instances  almost  to  the  caudal  extremity  of  the  medulla 
oblongata.  The  fibres  that  are  exposed  on  the  surface  form 
only  a  small  part  of  the  arciform  system  of  fibres,  as  those 
that  pass  from  the  nuclei  areuati  to  the  corpus  restiforme 
beneath  the  surface,  far  exceed  in  number  those  that  are 
on  the  surface.  In  stained  sections  of  the  medulla  ob- 
longata, just  cephalad  to  the  pyramlidal  decussation,  great 
bundles  of  these  arcuate  fibres  can  be  seen  in  the  ventro- 
lateral part  of  the  section,  converging  to  unite  with  the 
fasciculus  cerebellospinalis  to  form  the  corpus  restiforme. 
These  fibres  can  be  seen  in  sections  almost  as  far  sephalad 
as  the  olivae.     If  sections  are  made  through  the  central 


ANATOMY   OF    THE   BRAIN  101 

third  of  the  medulla  oblongata  as  shown  in  Plate  XXXV, 
and  examined,  stained  or  unstained,  a  wavy  mass  of  ap- 
parently structureless  material  is  seen  immediately  dorsad 
to  the  pyramis.  These  are  the  nuclei  arcuati,  extending 
for  about  5  mm.  on  either  side  of  the  raphe  where  they 
are  most  extensive. 

These  nuclei  extend  throughout  the  middle  third  of  the 
medulla  oblongata,  and  traced  cephalad  they  cease  some 
little  distance  eaudad  to  the  olivae.  It  must  be  remem- 
bered that  the  arcuate  fibres  join  those  of  the  fasciculus 
cerebellospinalis  and  go  to  the  corresponding  cerebellar 
hemisphere.  They  are  much  more  numerous  in  the  sheep 
than  in  man ;  the  nuclei  likewise,  are  infinitely  more  ex- 
tensive than  those  of  the  human  encephalon. 

This  system  of  fibres  and  nuclei,  obviously,  has  greater 
physiological  significance  in  the  sheep  than  in  man ;  per- 
haps they  are  association  centres  of  great  complexity  in 
structure  and  function;  presiding  over  complicated  sys- 
tems of  co-ordination  and  reflex  acts,  taking  the  place  of 
the  higher  reflex  centres  in  the  cerebrum  when  thiese 
become  functionless. 


U)2  ANATOJMV    OF    THE    BRAIN 


CHAPTER  XXVII. 


THE  MEDULLA  OBLONGATA  -  LATERAL  SUR 

FACE. 

There  is  nothing  particularly  striking  to  be  found  on 
the  lateral  aspect  of  the  medulla  oblongata.  At  the  caudal 
extremity,  if  the  specimen  be  viewed  from  the  side,  the 
ventral  surface  will  be  seen  to  bend  quite  suddenly  in  a 
dorsad  direction,  to  reach  the  medulla  spinalis  (Plate 
XXIV) .  The  fasciculus  lateralis  minor  is  plainly  seen,  and 
will  be  found  to  be  exceedingly  well  marked  as  it  reaches 
the  cord.  An  earnest  effort  should  be  made  to  identify 
this  structure,  and  to  determine  if  possible  its  cephalic 
destination.  Its  relations  as  it  is  traced  are  to  be  care- 
fully noted. 

Perhaps  the  easiest  way  to  begin  the  study  of  the  direc- 
tion of  the  tract  would  be  to  search  for  it  at  the  cephalic 
extremity  of  the  medulla  spinalis,  whence  it  can  be  fol- 
lowed with  comparative  ease.  The  sulcus  lateralis  ven- 
tralis  and  the  sulcus  lateralis  dorsalis  are  easily  identified; 
the  latter  sulcus  must  be  followed  cephalad,  where  '+  will 
be  seen  lying  between  the  tractus  spinalis  N.  trigemini  and 
the  corpus  restiforme.  Toward  its  cephalic  extremity  it 
becomes  very  indistinct  and  finally  ceases  at  the  cephalic 
border  of  the  trapezium. 

Lying  between  the  fasciculus  lateralis  minor  and  the 
sulcus  lateralis  dorsalis,  is  an  important  tract  called  the 
fasciculus  cereheUospinalis  (fig.  E),  because  it  runs  direct- 
ly to  the  corresponding  cerebellar  hemisphere  from  the 
medulla  spinalis.  This  fasciculus  is  frequently  called  the 
direct  cerebellar  tract  and  forms  part  of  the  inferior  cere- 
bellar peduncle  or  corpus  restiforme.  Traced  to  its  ter- 
mination it  will  be  found  to  pass  from  the  dorsal  part 
of  the  funiculus  lateralis  medullae  spinalis  to  the  medulla 
oblongata,  constituting  its  lateral  border  resting  between 
the  tractus  spinalis  N.  trigemini,  and  the  cephalic  termina- 
tion of  the  fasciculus  cuneatus  (see  Plate  XXIV).     Upon 


ANATOiMY    OP    THE    BRAIN  103 

reaching  the  lateral  extremity  of  the  trapezium,  it  bends 
dorsad,  winding  around  the  cephalic  border  of  the  N. 
acusticus,  and  then  turns  slightly  caudad  to  enter  the 
cerebellum  to  which  it  may  be  easily  traced. 

Just  dorsad  to  the  cephalic  extremity  of  the  fasciculus 
cuneatus  will  be  seen  a  modest  elevation  called  the  dava, 
to  be  again  referred  to,  and  mediad  to  the  cephalic  extrem- 
ity of  the  clava,  lying  close  against  the  N.  acusticus,  will 
be  observed  a  limited  view  of  the  area  acustica.  Note  how 
unmistakably  the  N.  acusticus  can  be  observed  entering 
the  dorsal  surface  of  the  medulla  oblongata. 

While  engaged  in  the  study  of  this  surface  of  the  medul- 
la oblongata,  some  very  interesting  structures  can  be  in- 
vestigated if  the  caudal  third  of  the  hemisphaerium  cere- 
bri be  removed  as  shown  in  Plate  XXI. 

It  would  be  well,  perhaps,  also  to  remove  the  hemisphae- 
rium cerebelli  and  the  flocculus  from  the  side  under  con- 
sideration;  this  dissection  is  easily  effected,  and  will  ex- 
pose the  parts  to  be  immediately  enumerated  as  shown 
slightly  enlarged  in  Plate  XXIV. 

Lying  against  the  convexity  of  the  corpus  restiforme  as 
it  winds  cephalad  of  the  N.  acusticus  will  be  found  a  large 
band  of  substantia  alba,  consisting  of  fibres  that  constitute 
the  .lajor  portion  of  the  pons.  This  bundle  is  the  brach- 
ium  pontis  (middle  cerebellar  peduncle)  and  these  fibres 
connect  the  two  cerebellar  hemispheres.  Some  of  these 
structures  have  been  noted  before  but  a  recapitulation 
showing  their  relations  to  the  medulla  oblongata  from  its 
lateral  aspect  will  do  no  harm. 

A  portion  of  these  fibres  may  be  separated  from  the  un- 
derlying strands  and  traced  by  teasing  to  the  medullary 
substance   of  the  hemisphaerium   cerebelli. 

Passing  caudad,  beneath  the  cephalic  border  of  the  bra- 
ehium  pontis  is  a  large  band  coming  from  beneath  the 
corpora  quadrigcmina,  called  the  brarhium  conjunctivum 
(superior  cerebellar  peduncle,  anterior  cerebellar  peduncle, 
crus  cerebelli  ad  corpora  quadrigemina)  ;  this  structure 
will  be  more  fully  described  while  considering  the  anatdiny 
of  the  vf^ntriv'Mlus  (|uartus. 


104  ANATOMY    OF    THE   BRAIN 

Winding  from  the  dorsal  to  the  lateral  surface  of  the 
brachium  conjunctivum  can  be  seen  the  N.  patheticus ;  this 
nerve  is  very  delicate  and  will  be  torn  from  its  attachment 
if  the  dissector  is  not  careful,  as  described  in  Chapter 
XXVI  while  discussing  the  roof  of  the  ventriculus  quar- 
tus.  The  hrachimn  quadrigeminum  inferius  is  plainly 
seen  running  along  the  dorsal  border  of  a  triangular  area 
called  the  trigonum  lemnisci  (Plate  XXIV).  The  three 
boundaries  of  this  space  are,  the  ventral  border  of  the  bra- 
chium quadrigeminum  inferius,  the  cephalic  border  of  the 
pons  and  the  dorso-caudal  border  of  the  pedunculus.  Pick 
up  some  of  these  fibres  of  the  leminiscus  lateralis,  and 
tear  them  in  a  cephalo-dorsad  direction.  They  wall  be 
seen  to  pass  between  the  brachium  conjunctivum  and  the 
brachium  pontis  to  the  lateral  extremity  of  the  trapezium 
with  the  fibres  of  which  they  seem  to  be  continuous.  This 
connection  between  the  trapezium  and  the  lemniscus  later- 
alis leading  to  the  colliculus  inferior  is  easily  demonstrated 
in  stained  serial  sections. 

■In  a  later  dissection  when  the  tractus  opticus  has  been 
removed,  this  brachium  can  be  distinctly  traced  by  Avay  of 
the  internal  capsule  to  the  caudal  extremity  of  the  hemi- 
sphaerium  cerebri  as  shown  in  Plate  XXII.  The  student 
must  endeavor  to  trace  this  brachium  when  he  is  demon- 
strating the  corona  radiata. 

At  the  point,  where  the  brachium  meets  the  pedunculus, 
look  for  the  tractus  peduncularis  transversus,  resting  in 
the  sulcus  between  the  colliculus  superior  and  the  pulvi- 
nar.  In  some  specimens  this  tract  appeared  traceable  to 
the  mesial  surface  of  the  colliculus  superior  into  the  sul- 
cus intercollicularis,  where  it  reaches  the  lamina  quadrige- 
mina;  it  then  changes  its  course  and  passes  directly  to- 
ward the  trigonum  habenulae. 

This  tract,  together  with  the  brachium  quadrigeminum 
inferius  and  the  caudal  border  of  the  tractus  opticus,  forms 
another  triangle,  trigonum  geniculatum,  which  contains 
the  corpus  geniculatum  externum.  As  the  tractus  pedun- 
cularis transversus  lies  in  the  most  dorsal  portion  of  the 


ANATOIMY    OF    THE    BRAIN  105 

sulcus,  it  is  very  indistinct,  but  in  a  few  cncephala  there 
can  be  no  doubt  as  to  its  existence  and  destination. 

The  tractus  opticus  is  particularly  well  shown  in  this 
dissection  as  it  passes  dorso-caudad  to  reach  the  pulvinar, 
corpus  greniculatum  externum  and  the  colliculus  superior. 

If  the  caudal  portion  of  the  hemisphere  be  cut  away  in 
an  oblifiue  direction,  and  the  dissection  carefully  done,  the 
structures  lying-  dorsad  and  caudad  to  the  pulvinar  will  be 
nicely  exposed  and  the  relations  of  the  pulvinar.  fascia 
dentata,  hippocampus,  and  the  cornu  inferius  ventriculi 
lateralis  clearly  shown    (Plate  XXI). 


106  ANATOMY    OF    THE    BRAIN 


CHAPTER  XXVIII. 


THE  MEDULLA  OBLONGATA-DORSAL  SURFACE. 

The  dorsal  aspect  of  the  iriednlla  oblongata  (Plate  XXV 
and  fig.  E),  is  of  more  than  ordinary  interest,  as  it  is 
largely  occupied  by  that  interesting  space  called  the  ven- 
triculus  quartus.  The  caudal  extremity  of  the  medulla 
oblongata  passes  into  the  cephalic  portion  of  the  medulla 
spinalis  quite  abruptly.  The  greater  difference  will  be 
seen  in  the  lateral  diameters.  The  caudal  third  of  the 
medulla  oblongata  does  not  enter  into  the  formation  of 
the  ventriculus  quartus,  and  the  description  of  that  por- 
tion not  entering  into  relation  with  the  ventricle  will  be 
completed  prior  to  the  consideration  of  those  parts  of  the 
medulla  that  are  so  intimately  associated  with  this  very 
important  ventricle. 

In  the  mid-dorsal  line  will  be  noticed  the  sulcus  dorsalis 
continued  cephalad  from  the  cord.  This  sulcus  is  pre- 
vented from  reaching  the  ventricle  by  an  arched  band  of 
tissue,  whose  convexity  is  directed  caudad,  called  the  ohex, 
beneath  which  there  is  a  cavity  called  the  "ventricle  of 
Arantius. ' ' 

This  obex  is  generally  quite  prominent,  and  little  diffi- 
culty will  be  experienced  in  finding  it.  As  the  sulcus 
dorsalis  reaches  the  obex  it  appears  to  divide  into  two 
rami  that  pass  latero-cephalad  in  opposite  directions,  em- 
bracing the  extremities  of  the  obex,  and  finally  to  disap- 
pear on  the  dorsal  surface  of  the  medulla  oblongata  at  a 
variable  distance  from  their  origin. 

On  either  side  of  the  little  triangular  space  formed  by 
the  obex  and  the  diverging  rami  of  the  sulcus  dorsalis,  is 
seen  a  very  delicate  fusiform  tract  of  substantia  alba,  for 
which  I  would  suggest  the  name  of  fasciculus  fusiformis. 
The  writer's  attention  was  first  called  to  the  possibility  of 
a  distinct  tract  in  this  region  from  the  peculiar  arrange- 
ment of  the  white  fibres  noticed  in  an  histological  section 
of  the  cord  located  about  5  mm.  from  the  medulla  oblon- 


ANATOMY   OF    THE   BRAIN  107 

gata  and  stained  with  haeniatoxylin.  The  position,  form, 
and  relation  of  this  fasciculus  can  be  easily  seen  with  the 
naked  eye  in  almost  all  stained  sections  of  the  cephalic 
extremity  of  the  medulla  spinalis. 

This  tract  in  section  is  clearly  shown  in  Plate  XXXIII, 
P,  and  in  making  sections  that  gradually  approach  the  me- 
dulla oblongata,  the  tract  increases  in  size  and  finally 
reaches  the  surface  by  way  of  the  proximal  extremity  of 
the  sulcus  dorsalis  as  illustrated  in  Plate  XXV. 

This  fasciculus  is  scarcely  perceptible  in  fresh  encephala, 
and  in  those  specimens  that  are  examined  directly  after  re- 
moval from  the  solution  of  formalin ;  after  macerating  the 
formalin-fixed  brain  in  water  for  one  or  two  weeks  the 
tract  is  easily  found. 

If  the  sulcus  dorsalis  be  gently  opened  the  dorsal  edge 
of  the  fasciculus  fusiformis  will  be  seen  skirting  the  wall 
of  the  sulcus  dorsalis,  diminishing  in  size  as  it  passes 
caudad;  the  dissector  should  not  neglect  to  discover  this 
fasciculus.  The  tract  can  be  seen  in  a  transverse  section  of 
the  cephalic  extremity  of  the  medulla  spinalis  with  the 
naked  eye  if  a  very  thin  section  be  made  with  a  sharp 
knife  and  the  section  viewed  while  held  up  to  the  light, 
but  not  direct  sunlight.  It  possesses  a  well  marked  nucleus 
that  is  easily  identified  in  stained  sections;  see  Plate 
XXXIV. 

The  sulcus  dorealis,  Plate  XXV,  is  bounded  on  each  side 
by  the  fasciculus  gracilis  (tract  of  Goll,  postero-internal 
tract),  which  passes  cephalad  and  ends,  when  it  reaches 
the  level  of  the  obex,  in  the  clava  which  assists  in  forming 
in  part  the  caudo-iateral  boundary  of  the  ventriculus 
quartus. 

Laterad  to  the  fasciculus  gracilis  can  be  seen  the  fascicu- 
lus cuneatus  (tract  of  Burdach,  postero-external  tract). 
These  two  fasciculi  are  separated  by  the  sulcus  intermedins 
dorsalis.  The  fasciculus  cuneatus  traced  cephalad  ends  in 
a  very  indi^^tinct  enlargement  in  some  specimens  called  the 
tuherculum  cuneatum.  The  tuberculum  cuneatum  is 
placed  more  caudad  than  the  clava,  as  illustrated  in  fig.  E. 
Within    the   substance   of   the   clava    and    the    tuberculum 


108  ANATOMY   OF    THE   BRAIN 

ciineatum  there  are  irregularly  arranged  masses  of  cells 
forming  nuclei.  The  substantia  grisea  that  eventually  de- 
velops into  the  nucleus  of  the  clava  is  derived  from  the 
grey  matter  of  the  cord,  as  an  exeresence  growing  dorsad 
into  the  cephalic  part  of  the  fasciculus  gracilis,  in  the 
same  manner  as  that  of  the  nucleus  cuneatus  in  the  human 
medulla  oblongata;  while  the  nucleus  of  the  fasciculus 
cuneatum  develops  independently.  The  three  nuclei,  viz., 
nucleus  fasciculi  fusiformi,  nucleus  fasciculi  gracilis  and 
the  nucleus  fasciculi  cuneati  can  be  seen  in  stained  sections 
just  caudad  to  the  entrance  of  the  canalis  centralis  into 
the  fourth  ventricle. 

From  these  nuclei  many  strands  of  fibres,  constituting 
the  deep  arciform  series,  can  be  easily  seen,  passing  in  an 
arched  direction,  ventro-mesiad  across  the  raphe,  where 
they  turn  cephalad,  forming  the  ventral  portion  of  the 
formatio  reticularis  alba.  This  band  of  fibres  as  it  passes 
toward  the  cerebrum  forms  the  mesial  lemniscus  or  fillet 
as  shown  in  Plates  XXXVI  and  XXXVII. 

These  inner  arching  fibres  can  be  seen  in  the  unstained 
section  if  sufficient  care  and  persistence  is  exercised. 

The  sulcus  intermedins  dorsalis  is  lost  on  the  lateral 
aspect  of  the  medulla  oblongata.  The  sulcus  lateralis  dor- 
salis runs  along  the  lateral  border  of  the  fasciculus  cu- 
neatus, separating  it  from  the  corpus  restiforme,  and  is 
the  line  of  origin  of  the  dorsal  nerve  roots  of  the  nervi 
cervicales  as  well  as  some  of  those  going  to  the  N.  vagus 
and  N.  accessorius.  Ventral  to  the  sulcus  lateralis  dor- 
salis lies  the  fasiculus  cerebellospinalis  passing  to  the 
lateral  area  of  the  medulla  oblongata,  forming  there,  as 
stated,  the  major  part  of  the  corpus  restiforme. 


DESCRIPTION  OF     FIG.     E. 

A.  Striae   inedullares    (N.    aciisticus).  /.  Clava     (caudal    exti'emity). 

B.  Plexus   ehorioideus   ventriculi    quarti.  J.  Fasciculus   gracilis. 

C.  Ranuis   obicis.  K.  Tuberculum     cuneatum. 

D.  Taenia   ventriculi    quarti.  L.  Fasciculus    cuneatus. 

E.  Trigonum   vagi.  M.  Sulcus    lateralis    dorsalis. 

F.  Trigonum    hypoglossi.  i\^  Fasciculus    cerebellospinalis. 

G.  Fasciculus    fusiformis.  S.  Nucleus    dorsalis   N.    cochlearis. 
//.  Obex. 


™-  '""'■"""  ''™3r:ut.u/'(o;sH5i"s*s.H'?^;^i.r''  -■"" "  "■• 


110  ANATOMY    OF    THE   BRAIN 


CHAPTER  XXIX. 

THE  FOURTH  VENTRICLE. 

The  ventriculus  quart  us  (fig.  E)  is  an  irregular  space 
lying  dorsal  to  the  pons,  the  trapezium'  and  the  cephalic 
two-thirds  of  the  medulla  oblongata.  Its  length  is  about 
17  mm.,  its  greatest  width  about  8  mm.,  and  its  depth  1 
m,  to  3  mm.  Its  roof  is  formed  cephalo-caudad  by  the 
velum  medullare  anterius  (valve  of  Vieussens),  vermis 
cerebelli  minor,  and  the  tela  chorioidea  ventriculi  quarti. 
A  portion  of  the  lateral  wall  at  the  cephalic  extremity  is 
formed  on  either  side  by  the  brachium  conjunctivum. 

The  distal  extremities  of  the  brachia  approach  the  mesial 
line  as  they  pass  caudad,  and  meet  in  the  medullary  sub- 
stance of  the  cerebellum,  forming  almost  a  complete  circle, 
as  shown  by  the  dotted  line  in  Plate  XXV.  This  circle  is 
completely  filled  in  or  closed  by  the  velum  medullare  an- 
terius. Further  caudad  the  lateral  boundaries  are  formed 
by  the  areae  acusticeae,  and  lastly  by  the  rami  of  the  obex 
and  a  small  portion  of  the  clava. 

'  The  sulcus  longitudinalis  fossae  rhomboideae  divides  the 
floor  of  the  ventricle  into  two  symmetrical  halves;  the 
cephalic  extremity  of  this  sulcus  leading  to  the  caudal 
opening  of  aquaeductus  cerebri,  and  its  caudal  limitation 
ending  at  the  entrance  of  the  canalis  centralis  into  the 
cord. 

The  fossa  rhomboidea  is  limited  on  each  side  by  the  sid- 
cus  limitans  fossae  rhomboideae.  Just  caudad  to  the  cen- 
tral part  of  the  floor  of  the  ventricle  will  be  seen  a  very 
narrow  bi-convex  area  called  the  eminentia  medialis,  with 
an  exceedingly  shallow  groove  running  longitudinally 
through  its  centre,  perhaps  a  continuation  of  the  sulcus 
longitudinalis  fossae  rhomboideae.  The  eminentia  medialis 
is  formed  by  the  stria  longitudinalis  profundis  (posterior 
longitudinal  bundle)  bending  dorsad  to  reach  the  floor  of 
the  ventricle.     (Plates  XXXVI  and  XXXVII.) 

This  eminence  in  some  cases  is  markedly  depressed  be- 


ANATOMY   OF    THE    BRAIN  111 

low  the  floor  of  the  ventricle  and  is  inclosed  on  either  side 
by  a  delicate  semilunar  sulcus;  it  is  in  all  probability  the 
homolo£i:ue  of  the  eminentia  niedialis  found  in  the  floor 
of  the  ventriculus  quartus  in  man.  The  eminence  is  clear- 
ly illustrated  in  Plate  XXV  and  Plate  XXXI,  figs.  2 
and  3,  and  fig.  E. 

The  cephalic  portion  of  each  lateral  half  of  the  ven- 
tricular floor  is  marked  by  a  distinct  spherical  elevation 
called  the  colliculus  facialis  {eminentia  facialis,)  beneath 
which  is  the  genu  nervi  facialis  and  to  which  the  N. 
facialis  can  be  easily  traced,  as  shown  in  Plate  XXX,  fig.  3. 

The  student  must  not  fail  to  make  an  incision  parallel 
to  the  cephalic  border  of  the  trapezium  extending  com- 
pletely through  the  structure  in  order  to  demonstrate  the 
course  of  this  nerve  as  it  passes  through  the  substance  of 
this  part  of  the  encephalon. 

Lateral  to  the  eminence  that  has  just  been  studied,  look 
for  a  triangular  depression  called  the  fovea  anterior. 
Caudad  to  this  fovea  the  sulcus  limitans  fossae  rhom- 
boideae  bends  toward  the  middle  line  along  the  mesial  bor- 
der of  quite  a  large  convex  elevation,  the  area  acustica; 
note  the  N.  acusticus  leading  down  to  it.  (See  Plate 
XXXVII.) 

At  the  caudad  extremity  of  the  ventricle  note  the  large 
mass  of  matter  lying  dorsad  to  the  entrance  of  the  canalis 
centralis,  the  obex  previously  mentioned;  with  its  convex- 
ity directed  caudad,  while  the  rami  obicis  pass  cephalad 
and  are  lost  to  view  as  they  reach  the  areae  acusticae. 
Where  the  inner  margins  of  these  rami  meet  the  mesial 
convex  borders  of  the  areae  acusticae  is  another  triangular 
depression,  the  fovea  posterior  (ala  cinerea).  (See  Plate 
XXXV.) 

On  each  side  of  the  caudal  portion  of  the  floor  of  the 
ventricle,  lying  between  the  sulcus  longitudinalis  fossae 
rhoraboideae  and  the  ramus  obicis,  is  a  longitudinally 
placed  eminence  called  the  eminentia  hypoglossi  (trigonum 
hypoglossi).  The  sulci  limitantes  fossae  rhombuideae  con- 
verge to  meet  the  sulcus  longitudinalis  fossae  rhomboideae 
at  the  caudal  extremity  of  the  v(uitriele  to  form  the  cala- 


112  AN  ATOMZ   OF    THE   BEAIN 

mus  scriptorius  (named  by  Herophilus,  3rd  Century 
B.  C). 

The  nucleus  alae  cinereae  which  embraces  the  nucleus 
vagus  and  the  nucleus  giosso-pharyngeus  is  situated  im- 
mediately lateral  to  the  fovea  inferior  and  the  caudal  ex- 
tremity of  the  sulcus  limitans  fossa  rhomboideae,  and  also, 
lies  in  part  beneath  the  well  marked  elevation  called  the 
trigonum  vagi  or  ala  cinerea.  Fibres  from  the  nucleus  N. 
glosso-pharyngeus  and  N.  vagi  can  be  traced  to  these 
nuclei  (Plate  XXXVI). 

The  trigonum  vagi  lies  ventrad  and  somewhat  mediad  to 
the  ramus  obicis  (fig.  E).  The  line  of  demarcation  be- 
tween the  trigonum  vagi  and  the  ramus  obicis  is  often  a 
well  marked  ridge  which  is  called  the  taenia  ventriculi 
quarti,  or  perhaps  it  is  homologous  with  the  fasciculus 
separans  of  the  human  brain. 

The  tissue  lying  laterad  to  the  fasciculus  separans  or 
taenia  is  non-nervous ;  and  on  section  has  a  vascular  or 
cavernous  appearance  (Plate  XXXV).  The  surface  of 
this  tissue  m)ay  be  called  the  area  postrema  of  Retzius. 

The  nucleus  alae  cinereae,  is  the  point  of  termina- 
tion of  the  sensory  fibres  of  the  N.  giossopharyngeus 
and  the  N.  vagus.  The  nucleus  ambiguus  is  found 
just  laterad  and  ventrad  to  the  fovea  posterior,  and  from 
this  nucleus  spring  the  motor  roots  of  the  same  two  nerves, 
together  with  some  of  those  of  the  N.  accessorius. 

The  tractus  spinalis  N.  trigemini  can  be  seen  7  mm. 
laterad  to  the  sulcus  longitudinalis  fossae  rhomboideae, 
with  its  concavity,  containing  the  nucleus  tractus  spinalis 
N.  trigemini,  directed  to  the  mesial  line.  Winding  around 
the  ventral  and  lateral  surfaces  of  the  tractus  spinalis  N. 
trigemini  is  a  very  thick  layer  of  fibres  running  in  a 
cephalo-laterad  direction  to  reach  the  corpus  restiforme 
as  shown  in  Plates  XXXVII  and  XXXVIII.  These  fibres 
are  plainly  seen  converging  from  the  nuclei  arcuati  toward 
the  corpus  restiforme  which  forms  a  very  prominent  struc- 
ture on  the  lateral  extremity  of  these  sections. 

About  3  mm.  cephalad  to  the  tip  of  the  calamus  scrip- 
torius,  as  a  very  slight  transverse   depression   the   sulcus 


AXATO.MV    (iK    THK    RKAIN  113 

traitsi^ersus,  extending  across  the  trigonum  hypoglossi, 
mai'king  off  an  area  of  tissue  the  shape  of  an  isosceles 
triangle  with  its  apex  pointing  to  the  entrance  of  the 
canalis  centralis  of  the  medulla  spinalis. 

Under  no  consideration  must  the  student  be  permitted 
to  leave  the  work  on  the  gross  anatomy  of  the  sheep's 
brain  without  making  a  series  of  coronal  sections  of  the 
encephalon  such  as  those  illustrated  in  Plates  XXVI  to 
XXXII,  inclusive. 

Drawings  should  be  made  and  all  the  parts  identified. 
These  preparations  are  of  great  value  in  fixing  in  the  stu- 
dent's mind  the  relationships  of  the  ganglia,  fasciculi  and 
other  points  of  interest  that  he  has  been  working  out  in 
the  foregoing  pages. 

It  would  be  well  worth  the  trouble  to  prepare  a  brain  by 
the  Kaiserling  method,  from  which  to  make  these  coronal 
sections,  for  there  will  be  difficulty  in  making  out  many  of 
the  points  of  interest  even  with  a  brain  that  has  been  care- 
fully prepared. 


PLATES  I- XL. 
[From  Drawings  {Excepting  I  and  II)  hy  the  Author] 


118  ANATOMY    OP    THE    BRAIN 


PLATES    I    AND    II. 

These  plates  represent  the  skull  of  the  sheep  one-half 
the  actual  size  of  the  preparation  and  reproduced  by 
photographs. 

PLATE  I  represents  the  dorsal  surface  of  the  skull. 

PLATE  II  shows  very  clearly  the  lateral  elevation  of 
the  entire  skull. 

These  two  plates  will  assist  the  student  in  removing 
the  brain  from  the  cranium,  by  giving  him  some  concep- 
tion of  the  place  to  make  the  first  incision,  and  how  the 
further  operations  are  to  be  carried  on. 


ANATOMY   OF    THE    BRAIN  119 


PLATE  I -DORSAL  AREA  OF  THE  SKULL 


120  ANATOMY    OF    THE   BRAIN 


PLATE    II. 

Lateral  Elevation  of  the  Sknll. 


I'lwXTK   II     LATERAL    AREA    OF    THE    SKTILL 


122  ANATOMY    OF    THE    BRAIN 


PLATE    III. 

THE  ENCEPHALON. 

This  illustration  is  designed  to  give  an  idea  of  the 
appearance  of  the  eneephalon,  inclosed  within  the  dura 
mater,  the  calvarium  having  been  removed.  Two  of  the 
sinuses  have  been  opened,  as  they  ought  to  be  if  the 
directions  for  dissecting  them  are  carried  out.  Note  the 
tubular  process  extending  caudad  over  the  medulla 
spinalis. 

A.  Bulbi  olfactorii. 

B.  Triangular  thickening. 

C.  Vena  frontalis. 

D.  Pissura  cruciata. 

E.  Fissura  cerebri  lateralis.     (Sylvius.) 

F.  Sinus  sagittalis. 

G.  Vena  cerebri  magna.     (Galen.) 
H.     Confiuens  sinuum. 

I.      Sinus  transversus. 

J.      Vermis  cerebelli. 

K.     Hemisphaerium  cerebelli. 


ANxVTO:\[V    f)F    lUK    BRAIN 


123 


PLATE  I  IT- DORSAL  A'^'ECT  OF  DURA  MATER 

(x  1  2/3). 


124  ANATOMY    OP    THE    BRAIN 


PLATE  IV. 

THE  CIRCULUS  ARTERIOSUS. 

The  eirculiis  arteriosus  (Willisii)  as  shown  in  this  draw- 
ing can  be  worked  out  on  most  encephala  where  the  arter- 
ies have  not  been  injected.  It  is  a  little  difficult  some- 
times to  identify  the  arteria  cerebri  propria  because  it 
divides  immediately  after  entering-  the  brain  cavity. 

A.  Arteria  cerebri  anterior. 

B.  Arteria  communicans.       r' 

C.  Arteria  cerebri  media. 

D.  Ramus  anterior. 

E.  Ramus  posterior. 

F.  Arteria  cerebri  posterior. 

G.  Arteria  basalaris. 

H.  Arteria  cerebelli  anterior. 

/.  Arteria  cerebelli  posterior. 

X.  Arteria  cerebri  propria. 

Z.  Arteria  basilaris  gangliaformis  posterior. 


ANATO^ilY    OF    THE    BRAIN 


125 


PLATE  IV— ARTEKIKS  ON  VENTRAL  SURFACE 
OF  THE  BRAIN  (x   1  2/3). 


126  ANATOMY   OP   THE   BRAIN 


PLATE  V. 

FACIES  DORSALIS  CEREBRI  ET  CEREBELLI. 

A.  Fissura  longitudinal] s. 

B.  Sulcus  coronalis. 

C.  Fissura  cruciata. 

D.  Fissura  cerebri  lateralis.     (Sylvius.) 

E.  Fissura  suprasylvia. 

F.  Sulcus  lateralis. 

G.  Sulcus  intermedia. 
H.  Sulcus  medialis. 

I.  Fissura  cerebelli  superior. 
/.  Fissura  cerebelli  medialis. 
K.  Fissura  cerebelli  inferior. 
L.  Medulla  oblongata. 

M.  Sulcus  dorsalis. 

Z.  Polus  posticus. 

1.  Gyrus  frontalis  superior. 

5,  Gyrus  frontalis  medialis. 

3.  Gyrus  sylviacus   (arcuatus). 

4.  Gyrus  lateralis. 

5.  Gyri  mediales. 

6.  Gyrus  internus. 

7.  Vermis  cerebelli. 

8.  Flocculus. 

9.  Parafiocculus. 

10.     Lobus  superior  (hemisphaerium  cerebelli). 

II.  N.  cervicalis  I. 
12.  Medulla  spinalis. 


PLATE   V-DOKSAL  SURFACE  OF  J'HE  BRAIN 

(X  1  2/8). 


128  ANATOMY   OF   THE   BRAIN 


PLATE  VI. 

FACIES  LATERALIS  CEREBRI  ET  CEREBELLI. 

A.  Gyrus  frontalis  inferior. 

B.  Gyrus  orbitalis. 

C.  Tractus  olfactorius. 
G.  Fissura  rhinalis. 

H.  Gyri  centrales   (Island  of  Reil). 

7.  Fissura  cerebri  lateralis  (Sylvii). 

J.  Ramus  posterior  fissurae  cerebri  lateralis. 

W.  Ramus  anterior  fissurae  cerebri  lateralis. 

Z.  Lobus  hippocampi. 

3.  Gyrus  sylviaeus  (arcuatus). 

7.  Vermis  cerebelli. 

8.  Lobus  cerebelli  inferior. 

9.  Lobus  cerebelli  medialis  (paraflocculus). 

10.  Lobus  cerebelli  superior  (hemisphaerium  cerebelli). 

11.  Flocculus. 


ANATOMY    OF    THE    BRAIX 


129 


PLATE  VI-LATP:RAL  SURFACE  OF  THE  BRAIN. 


130  ANATOMY    OF    THE    BRAIN 

PLATE  VII. 
VENTRAL  SURFACE  OF  THE  ENCEPHALON. 

A.  Fissiira  sagittalis. 

B.  Gyrus  orbitalis. 

C.  Substantia  g'risea  radicis  lateralis. 

D.  Radix  medialis  bulbi  olfactorii. 

E.  Substantia  alba  radieis  lateralis. 

F.  Locus  perforatus  anterior. 

G.  Fissura  rhinalis. 
H.  Insula. 

/.  Fissura  cerebri  lateralis. 

J.  Infundibulum. 

K.  Chiasma  opticum. 

L.  Traetus  opticus. 

M.  Corpus  mamillare. 

N.  Traetus  peduncularis  transversus. 

0.  Nucleus  interpeduncularis. 

P.  Pedunculus  cerebri. 

Q.  Pons. 

R.  Trapezium. 

S.  Oliva. 

T.  Fasciculus  lateralis  minor. 

U.  Medulla  oblongata. 

V.  Radix  spinalis  nervi  accessorii. 

W.  Ramus  anterior  fissura  cerebri  lateralis. 

Y.  Sulcus  ventralis  medullae  oblongatae. 

Z.  Lobus  hippocampi. 

1.  Bulbus  olfactorius. 

2.  N.  opticus. 

3.  N.  oculomotorius. 

4.  N.  trochlearis. 

5.  N.  trigeminus.  • : 

6.  N.  abducens.  ' 

7.  N.  facialis. 

8.  N.  acusticus.  '  ■  -'' 

9.  N.  giossopharyngeus. 
10.  N.  vagus. 

li.  N.  aceessorius. 

12.  N.  hypoglossus. 

13.  Radix  aseendens  N.  trigemini. 


ANATOMY    OF    THE    BRAIN 


131 


PLATE  VIT  VENTRAL  SUREACE  OE  THE  BRAIN 

(x   1  2/3). 


l!^2  ANATOMY    OP    THE    BRAIN 


PLATE  VIII. 

FACIES  MEDIALIS  CEREBRI. 

A.  Rostrum  corporis  callosi. 

B.  Genu  corporis  callosi. 

C.  Bulbus  olfactorius. 

D.  Sulcus  cinguli. 

E.  Gyrus  intermedius. 

F.  Sulcus  parolfactorius. 

G.  Gyrus  marginalis  anterior. 
H.  Gyrus  cinguli. 

/.  Corpus  callosum. 

/.  Sulcus  corporis  callosi. 

K.  Gyrus  marginalis  posterior. 

L.  Sulcus  splenialis. 

M.  Splenium  corporis  callosi. 

N.  Colliculus  superior. 

0.  Corpus  medullare  cerebelli. 

P.  Ventriculus  quarti. 

Q.  Canalis  centralis. 

R.  Lamina  quadrigemina. 

8.  Corpus  pineale. 

T.  Commissura  posterior. 

U.  Fasciola  cinerea. 

V.  Trigonum  habenulae. 

W.  Corpus  fornicis. 

X.  Massa  intermedia  (commissura  media] is ; 

Y.  Tuber  cinereum. 

Z.  Commissura  anterior. 

2.  Radix  medialis  bulbi  olfactorii. 


ANATOMY   OF    THE   BRAIN 


133 


PLATE   VIII-MESIAL  SURFACE   OF   THE  BRAIN. 


134  ANATOMY    OF    THE    BRAIN 


PLATE  IX. 

FASCIES  ANTERIOR. 

This  figure  represents  the  encephalon  when  it  is  looked 
at  from  a  point  directly  cephalad.  This  plate  together 
with  Plates  V,  VI  and  VII,  will  give  a  very  clear  idea 
of  the  general  shape  and  detailed  appearance  of  the  ex- 
terior of  the  encephalon. 

A.  Gyrus  frontalis  medialis. 

B.  Sulcus  coronalis. 

C.  Fissura  cerebri  lateralis. 

D.  Gyrus  sylviacus. 

E.  Fissura  erueiata. 

F.  Fissura  sagittal  is. 

G.  '  Gyrus  frontalis  superior. 
H.     Fissura  suprasylvia. 

J.      Insula. 

L.     Lobus  hippocampi. 

0.     Lobus  olfaetorius. 


ANATOMY   OP   THE   BRAlN 


135 


PLATE  IX-ANTERIOR  SURFACE  OF  THE 
BRAIN  (x  1  2/3). 


136  ANATOMY   OF    THE   BRAIN 


PLATE  X. 

EXTENSION  OF  FISSURES  AND  SULCI  INTO  THE 
HEMISPHERES. 

This  illustration  is  introduced  to  convey  some  idea  of 
the  relatively  great  superficial  area  provided  by  the  ex- 
tension of  fissures  and  sulci  into  the  substance  of  the 
hemispheres.  It  must  also  be  noted  that,  wherever  the 
depressions  go,  there  follows,  a  corresponding  quantity 
of  substantia  grisea,  and  that  this  substantia  grisea  is 
composed  of  innum,erable  nerve  cells,  the  physiological 
units  of  all  nerve  tissue. 

It  is  self  evident  that  the  area  thus  provided  affords 
accommodation  for  a  vastly  greater  number  of  cells  than 
would  be  possible  were  the  surface  of  the  cerebrum  un- 
convoluted. 


ANATOMY   OF    THE   BRAIN 


1:17 


ATE   X-SEC1'I0N   OF  CEREBRUM  TO   SHOW 
OKAY  AXO  WIIITP:  MA'nWOH  (x  1  2/3). 


138  anatojMY  of  the  brain 


PLATE  XI. 

COURSE  OF  THE  FIBRES  OF  THE  CORPUS  CAL- 

LOSUM. 

This  dissection  was  made  to  convey  to  the  student  some 
idea  of  the  course  taken  by  the  fibres  of  the  corpus  eal- 
losum  in  its  various  parts. 

A.  Genu  corporis  callosi. 

B.  Stria  longitudinalis  medialis. 

C.  Stria  longitudinalis  lateralis. 
Z>,     Corpus  callosum. 

E.  Fibres  of  the  caudal  portion  of  the  corpus  cal- 
losum after  they  have  changed  their  course  and  proceed 
cephalad  toward  the  cephalic  extremity  of  the  lobus  hip- 
pocampi, covering  the  cornu  inferius  ventriculi  lateralis. 

F.  Splenium  corporis  callosi. 

G.  Corpus  pineale. 

H.     Colliculus  superior. 


ANATO:\rY    OF    THE    BRAiN 


139 


PLATE    XI     ("OKPUS    CALLOSUM,    DORSAL    SUR 
FACE   fx  1  2/3). 


140  ANATOMY   OF   THE   BEAIN 


PLATE  XII. 

FIBRES   OF  THE  CORPUS   CALLOSUM  AND   STRI- 
ATED CONSTRUCTION. 

Represents  many  features  that  are  similar  to  those 
shown  in  the  preceding  cut,  emphasizing  more  particu- 
larly perhaps  the  striated  construction  of  the  corpus  ca]- 
losum. 

A.  The  cephalic  extremity  of  the  transverse  fibres  of 
the  splenium  corporis  callosi,  as  they  lie  over  the  cephalic 
extremity  of  the  cornu  inferius  ventriculi  lateralis.  A 
large  opening  is  shown  through  that  portion  of  the  spleni- 
um which  covers  in  the  caudalie  portion  of  the  ventriculus 
lateralis,  and  the  beginning  of  the  cornu. 

B.  Fasciculus  subcallosus. 

C.  Hippocampus. 


anato:j[y  of  the  brain 


141 


I^LATE  XII -CORPUS  CALLOSUM,  SHOWING  RAD- 
IATING FIBRES  OF  THE  SPLENIUM 

(x  1  2/3). 


142  ANATOMY    OF    THE   BRAIN 


PLATE  XIII. 

DISSECTION  FOR  THE   CAVITIES   OF  THE   VEN- 
TEICULI  LATERALES. 

Illustrating  the  necessary  dissections  that  are  to  be 
made  to  expose  the  cavities  of  the  ventriculi  laterales,  and 
the  structures  forming  their  floors. 

A.  Cornu  anterius  ventriculi  lateralis. 

B.  Nucleus  eaudatus. 

C.  Corpus  callosum.  Hanging  from  this  portion  of 
the  corpus  callosum  will  be  seen  the  septum  pellucidum, 
separating  the  two  ventricular  cavities;  the  septum  pel- 
lucidum hangs  :from  the  ventral  surface  and  is  not  shown 
in  this  drawing. 

D.  "V.  corporis  striati. 

E.  Recessus  triangularis. 

F.  Corpus  fornicis. 

G.  Plexus  chorioideus  ventriculi  lateralis. 
H.     Hippocampus. 

I.      Cingulum  inferius   (fasciculus  subcallosus). 
J.      Cornu  inferius  ventriculi  lateralis. 


ANATOMY   OF    THE   BRAIN 


143 


PLATE    XIIl-LATEl^AL    VENTKICLES     OF    THE 
BRAIN  (x  1  2/3). 


144  ANATOMY   OP   THE   BRAIN 


PLATE  XIV. 

CONNECTIONS  OF  THE  VENTRICULI  LATERALES 
AVITH  VENTRICULUS  TERTIUS. 

This  is  designed  for  the  purpose  of  shovang  the  passages 
that  apparently  connect  the  ventriculi  laterales  with  the 
ventriculus  tertius  and  the  structures  that  pass  through 
them.  The  corpus  callosum  and  the  central  portion  of 
the  corpus  fornicis  have  been  removed. 

A.  Septum  pellucidum. 

B.  Colurana  fornicis. 

C.  V.  terminalis. 

D.  Foramen  interventriculare  (foramen  of  Monroe) 
containing  the  V.  terminalis  and  the  plexus  chorioideus 
ventriculi  lateralis  on  its  way  from  the  ventriculus  lat- 
eralis to  become  the  plexus  chorioideus  ventriculi  tertii. 
The  margin  of  the  corpus  fornicis  has  been  cut  away  on 
the  left  side  to  expose  the  fissure. 

E.  V.  cerebri  interna. 

F.  Plexus  chorioideus  ventriculi  lateralis. 

G.  Margo  corporis  fornicis. 
H.     V.  cerebri  magna  (Galen). 

I.      Plexus  chorioideus  ventriculi  tertii. 
J.      Hippocampus. 


ANATOMY    OP    THE    BRAIN 


145 


PLATE   XIV- THIRD    VENTRICLE    AND    CHOROID 
PLEXUS  (x  1  2/3). 


146  ANATOMY   OF   THE   BRAIN 


PLATE  XV. 

THE  VENTRICULUS  TERTIUS  AND  THE  VEN- 
TRICULI  LATERALES, 

after  the  corpus  fornicis  and  the  tela  ehorioideus  ventrie- 
uli  lateralis  with  its  plexus  have  been  removed. 

A.  Columna  fornicis. 

B.  Ventriculus  tertius   (corpus  fornicis  removed). 
G.     Thalamus. 

D.  Stria  meduUaris  thalami. 

E.  Fimbria  hippocampi. 

F.  Pulvinar. 

G.  Corpus  pineale. 

H:     Colliculus  superior. 


ANATOMY    OF    THE    BRAIN 


147 


PLATE   XV-LATP:KAL  AND   THIRD  VENTRICLES 
OF  THE  BRAL\  (x  1  2/3). 


148  ANATOMY   OF   THE   BRAIN 


PLATE  XVI. 

ANOTHER    STEP    IN    THE    DISSECTION    OF    THE 

VENTRICULUS  LATERALIS, 
exposing   the   hippocampus,   fimbria  hippocampi   and   the 
plexus  ehorioideus  attached  to  the  pia  seen  passing  into 
the   cavity   through   the   fissura    transversa   as   they  pass 
ventrad  into  the  cornu  inferior  ventriculi  lateralis. 

A.  Septum  pellucidum. 

B.  Columna  fornieis. 

C.  Recessus  triangularis. 

D.  Plexus  ehorioideus  ventriculi  lateralis. 

E.  Corpus   fornieis. 

F.  Hippocampus. 

G.  Fibres  of  the  splenium. 

H.  Cingulum   inferius    (fasciculus  subcallosus). 

/.  Fimbria  hippocampi. 

J.  Plexus  ehorioideus. 

L.  Stria  terminalis. 


ANATOMY   OF   THE    BRAIN 


149 


PLATE   XVI-FORXIX,    HIPPOCAMPUS    AND    CIN- 
GULUM  INFERIOR   (x  1  2/3). 


150  ANATOMY    OP   THE   BRAIN 


PLATE  XVII. 

DISSECTION    SHOWING    THE    MESIAL    SURFACE 
OF  THE  LOBUS  HIPPOCAMPI  AND  THE 
FASCIA  DENTATA 
as  they  wind  around  the  crus  cerebri. 

A.  Radix  medialis  bulbi  olfactorii. 

B.  Commissura  anterior. 

C.  Cephalic  extremity  of  the  lobus  hippocampi. 

D.  Crus  cerebri   (transverse  section). 

E.  Fascia  dentata. 

F.  Fissura  dentata. 

G.  Fasciola  cinerea. 

H.  Stria  medullaris  thalami. 

/.  Thalamus. 

J.  Foramen  interventriculare. 

K.  Ventriculus  lateralis. 

L.  Nucleus  eaudatus. 

M.  Gyrus  cinguli. 


ANATOMY   OF   THE   BRAIN 


151 


PLATP]    XVII-FASCIA    DENTATA    AND    MESIAL 
ST'KFACE  OF  TWE  HIPPOCAMPUS  (x  1  2/3). 


152  ANATOMY   OF   THE   BEAIN 


PLATE  XVIII. 

SECTION  OF  THE  CORPUS  STRIATUM  AND  THAL- 
AMUS. 

A  composite  drawing-  illustrating  a  horizontal  section  of 
the  corpus  striatum  and  the  thalamus. 

A.  Nucleus  caudatus. 

B.  Substantia  alba  insulae. 

C.  Nucleus  lentiformis. 

D.  Capsula  externa. 

E.  Claustrum. 

F.  Capsula  interna. 

G.  Substantia  grisea  insulae. 
H.     Area  medialis  thalami. 

I.  Ventriculus  tertius. 

J.  Area  lateralis  thalami. 

K.  Pars  centralis  thalami. 

L.  Trigonum  habenulae. 

M.  Area  posterior  thalami. 

N.  Corpus  pineale. 

0.  Fascia  dentata. 

P.  Fissura  dentata. 

Q.  Colliculus  superior. 

R.  Cornu  inferius  ventriculi  lateralis. 

^.  Genu  capsulae  internae. 


ANATOMY    OF    THE    BRAIN 


153 


PLATE  XVI J 1      rilK  CORPUS  STRIATUM 

(X  1  2/3). 


154  ANATOMY    OF    THE   BRAIN 


PLATE  XIX. 

FIBRES  OF  THE  COMMISSURA  ANTERIOR. 

This  dissection  shows  particularly  well  the  course  taken 
by  the  greater  number  of  fibres  that  constitute  the  com- 
missura  anterior.  The  drawing  represents  the  central  por- 
tion of  the  commissure  located  about  5  cm.  dorsad  to  the 
chiasma  opticum.    The  hypophysis  is  also  shown. 

A.  Radix  medialis  bulbi  olfactorii. 

B.  Commissura  anterior^  or  commissura  olfactoria. 
H.     Hypophysis. 

J.      Infundibulum. 


ANATOMY   OF    THE    BRAIN 


155 


PLATK  XiX-THE  ANTEKiOK  COMMISSURE 

(x  1  2/3). 


156  ANATO]\rY    OP    THE   BRAIN 


PLATE  XX. 

THE  DISSECTION  OF  THE  COLUMNAE  FORNICIS. 

A.  Pars  libera  columnie  fornicis. 

B.  Septum  pellucidum    (in  part). 

C.  Substantia  grisea. 

D.  Commissura  anterior. 

E.  Pars  tecta  columnae  fornicis. 

F.  Fasciculus  thalamomamillaris. 

G.  Corpus  mamiliare. 
H.  Lamina  pinealis. 

J.      Aquaeductus  cerebri. 
K.     Commissura  posterior. 


ANATOMV^    OF    THE    BRAIN 


157 


l^.BM.  ^ 


l^LATE  XX-PILLARS  OF  THE  FORNIX. 


158  ANATOMY  OF   THE  BRAIN 


PLATE  XXI. 

An  oblique  section  of  the  caudalic  portion  of  the  cere- 
brum has  been  removed  to  expose  the  following  struc- 
tures in  situ. 

A.  Colliculus  superior. 

B.  Cornu  inferius  ventrieuli  lateralis. 

C.  Hippocampus. 

D.  Fascia  dentata. 

E.  Pulvinar. 

F.  Tractus  opticus. 

G.  Corpus  geniculatum  externum. 
H.  Tractus  peduncularis  transversus. 
I.  Brachium  quadrigeminum  inferius. 
J.  Colliculus  inferior, 

0.  Corpus  geniculatum  externum. 


AXATOMY   OP    THE   BRAIN 


159 


PLATE    XXI-PROXIMAL    TER:^nNATION    OF    OP- 
TIC TRACT. 


160  ANATOMY   OF   THE   BRAIN 


PLATE  XXII. 

THE  CORONA  RADIATA. 

A.  Hippocampus. 

B.  Fimbria  hippocampi. 

C.  Portion  of  corona  formed  in  part  by  the  brachium 
quadrigeminum  inferius. 

D.  Portion  formed  at  the  genu  by  the  pyramis  anterior. 

E.  Portion  formed  by  the  mesial  fibres  of  the  pyramis 
anterior. 

P.  Infundibulum  and  corpus  mamillare. 

G.  Tracticus  opticus. 

/.  Brachium  quadrigeminum  inferius. 

J.  Lateral  fibres  of  the  crus  cerebri,    (trigonum  lem- 
nisci). 

K.  Brachium  conjunctivum. 

L.  Pyramis  anterior,  some  fibres  of. 


ANATOMY   OF    THE   BRAIN 


161 


PLAICE  XXn~THP]  CORONA  RADIATA. 


162  ANATOIMY   OP   THE   BRAIN 


PLATE  XXIII. 

VENTRAL  SURFACE  OF  THE  PONS,  TRAPEZIUM, 
AND  MEDULLA  OBLONGATA. 

A.  Pons. 

B.  Sulcus  basilaris. 
G.     Flocculus. 

D.  Trapezium. 

E.  Oliva. 

F.  Pyramis  ventralis. 

G.  Ramus  aseendens  N.  trigemini,   (tractus  spinalis  N. 
trigemini). 

H.  Fasciculus  lateralis  minor. 

/.  Sulcus  ventralis  lateralis. 

J.  Funiculus  lateralis. 

K.  N.  acccssorius  (spinal  portion). 

L.  Sulcus  ventralis. 

N.  Ligamentum  denticulatum. 

0.  Pia. 

5.  N.  trigeminus    (the  larger  is  the  sensory  and  the 
smaller  the  motor  portion). 

6.  N.  abdueens. 

7.  N.  facialis. 

8.  N.  acusticus. 

9.  N.  glossopharyngeus. 

10.  N.  vagus. 

11.  N.  accessorius. 

12.  N.  hypoglossus. 


ANATOMY   OF    THE   BRAIN 


16.1 


I ' I . A  T 1 :     X  X  I  f  [  -  VENTRAL    SUR  l^^\CK     OF    PONS, 

TKAI'IOZKIM  ANJ)  MEDULiiA  OIUjON- 

(JA^'A   (x  2  2/3). 


164  ANATOMY    OF    THE    BRAIN 


PLATE  XXIV. 

LATERAL  SURFACE  OF  THE  CRUS  CEREBRI, 
PONS,  TRAPEZIUM,  AND  THE  MEDUL- 
LA OBLONGATA. 

A.  Corpus  geniciilatuin  internum. 

B.  Tractus  opticus. 

C.  Fascies  medialis  cruris  cerebri. 

D.  N.  oculomotorius. 

E.  Tractus  peduncularis  transversus. 

F.  Tractus  pyramis  pedunculi  cerebri. 

G.  Braehium   quadrigeminum  inferius  or  tractus  cere- 
bro-thalmieus. 

H.  N.  patheticus. 

/.  Pons. 

J.  N.  trigeminus. 

K.  N.  abducens. 

L.  Trapezium. 

M.  N.  facialis. 

N.  Tractus  lateralis  minor. 

0.  Oliva. 

P.  Pyramis. 

Q.  Funiculus  lateralis. 

B.  Sulcus  lateralis  ventralis. 

S.  Sulcus  lateralis  dorsal  is. 

T.  Fasciculus  euneatus. 

V.  Clava. 

V.  Corpus  restiforme. 

W.  N.  acusticus. 

X.  Portio  motor  N.  trigemini. 

Y.  Braehium  pontis. 

Z.  Braehium  conjunctivum. 

1.  Colliculus  inferior. 

2.  Colliculus  superior. 

3.  Corpus  pineale. 

4.  Pulvinar.  .  i 

5.  Tractus  spinalis  N.  trigemini. 

6.  Trigonum  lemnisci. 


IMiATPJ     XXlV-l.A'J'KJiAL     SURFACE     OF     CRUS 

cerp:br[.  pons,  ^irapezium,  and  med- 
ulla OBI.OXtiATA   (x  2  2/3). 


16G  ANATOMY   OF   THE   BRAIN 

PLATE  XXV. 

DORSAL  SURFACE  OF  THE  MEDULLA  AND  PONS, 

WITH  FLOOR  OF  THE  VENTRIC- 

ULUS  QUARTUS. 

A.  Ventriculus  tertius. 

B.  Stria  medullaris  thalami. 

C.  Piilvinar. 

D.  Corpus  pineale. 

E.  Corpus  geniculatum  iuteruuin. 

F.  Sulcus  intercollicularis, 

G.  Colliculus  superior. 
H.  N.  patheticus. 

I-X.     Sulcus  limitans  fossae  rhomboideae. 

J.  Colliculus  inferior. 

K.  N.  trigeminus. 

L.  Colliculus  facialis. 

M.  Fovea  anterior. 

N.  Brachium  conjunctivum. 

0.  Sulcus   long'itudinalis   fossae    rhoiuboideae. 

P.  Brachium  pontis. 

Q.  Tuberculuin  acusticum. 

R.  Fossa  rhomboidea. 

;S^.  Sulctls  semilunaris. 

T.  Corpus  restiforme. 

V.  Area  aeustica. 

V.  Fovea  posterior. 

W.  Eminentia  medialis. 

Y.  Clava. 

Z.  Canalis  centralis  medullae  spinalis. 

1.  Obex. 

2.  Depressio  interfusiformis. 

3.  Sulcus  fusiformis. 

4.  Fasciculus   fusiformis. 

5.  Sulcus  intermedins  dorsal  is. 

6.  Fasciculus  gracilis. 

7.  Sulcus  dorsalis. 

8.  Fasciculus  cuneatus. 

9.  Sulcus  lateralis  dorsalis. 

10.     Fasciculus   eerebellospinalis. 


A 

j^ai^fek'A  ^fe, 

M 

i 

KgH 

G-V 


R'li 


PLATE   XXV^-DOKSAh   SURFACE    ()K    PONS    AND 
THE  MEDULLA  OBLONGATA  (x  2  2/3). 


168  ANATOMY   OF    TIIE   BRAIN 


PLATE  XXVI. 

Fig.    1.     A    CORONAL    SECTION    THROUGH    THE 
BULBI  OLFACTORII, 

beginning  on  the  dorsal  surface  of  the  encephalon  near 
the  narrowest  portion  of  the  gyrus  medialis  anterior. 

A.  Fissura  iongitudinalis. 

B.  Fissura  coronalis. 

C.  Gyrus  frontalis  inferior. 

D.  Gyrus  orbitalis. 

F.     Ventriculus  bulbi  olfactorii. 
P.     Bulbus  olfactorius. 


Fig.   2.      A    SECTION    THROUGH    THE    CEPHALIC 
PORTIONS  OF  THE  VENTRICULI  LATER- 
ALES  AND  SEPTUM  PELLUCIDUM, 

beginning  in  the  fissura  coronalis. 
A.     Fissura  Iongitudinalis. 
G.     Corpus  callosum. 
/.      Septum  pelluciduui. 
/.      Nucleus  caudatus. 
K.     Capsula  interna. 
L.     Tractus  olfactorius. 
M.    Rostrum  corporis  callosi. 
N.     Capsula  externa. 
0.     Ventriculus  lateralis. 


Fi"-.    l-Cdtoiial    Section    'rhr()U«j:li    the    Olfactory    Bulbs 


Fi^-  2— Section  Tliroutih   Anterior  Portion  of  tho  Lateral 
Ventricles  (x  2). 
PLATE  XXVI. 


170  ANATOMY   OF   THE   BRAIN 

PLATE  XXVII. 

Fig.    1.      CARRY    THE    SECTION    THROUGH    THE 
ENCEPHALON, 

parallel  to  and  just  cephalad  to  the  fissura  cerebri  lat- 
eralis. 

A.  Fissura  longitudinalis. 

E.  Fissura  suprasylvia. 

F.  Nucleus  lentiformis. 

G.  Corpus  callosum. 
K.  Insula. 

/.  Septum  pellucidum. 

K.  Capsula  interna. 

iV.  Capsula  externa. 

0.  Ventriculus  lateralis. 

Q.  Substantia  alba  insulae. 

jR.'  Ramus  anterior  fissurae  lateralis  cerebri. 

B.  Claustrum. 

T.  Commissura  anterior. 

3.  Nucleus  caudatus. 

W.  Stria  terminalis. 

77.  Columna  fornicis. 

Fig.   2.     BEGIN  THE  INCISION  ON  THE  DORSAL 
SURFACE  OF  THE  ENCEPHALON 

about  midway  between  the  fissura  cruciata  and  polus  pos- 
ticus, completing  the  section  cephalad  to  the  opening  in 
the  infundibulum. 

A.     Fissura  longitudinalis. 

E.     Fissura  suprasylvia. 

G.     Corpus  callosum. 

J.      Ventriculus  tertius. 

K.     Capsula  interna. 

L.     Recessus  opticus  ventriculi  tertii. 

0.     Ventriculus  lateralis. 

P.     Thalamus. 

R" .  Ramus  posterior  fissurse  lateralis  cerebri. 
■    V.     Corpus  fornicis. 

X.     Fasciculus  subcallosus. 

Y.     Plexus  chorioideus  ventriculi  tertii. 

Z.     Substantia  intermedia. 

1.  Tractus  opticus. 

2.  Infundibulum. 

4.  Lobus  hippocampi. 

5.  Fissura  dentata. 


AXATO:\[A'   OF   THE   BRAIN 


171 


Fig.  1  —  Section  -lust  Posterior  to  tho   Fissure  of   Svlviiis 

(x  2). 


i^U 


Fij?.  2— Section  Throu<>li  Sub>stautia  Iiitennedia   (x  2;. 
PLATE  XXVII. 


172  ANATOMY   OF    THE   BRAIN 


PLATE  XXVIII. 

Fig.  1.      BEGIN  THE  INCISION  6  MM.  CAUDAD  TO 

THE  LAST  SECTION, 
reaching  the  ventral  surface  just  caudad  to  the  infundib- 
ulum. 

A.     Fissura  longitudinal  is. 

C.     Fasciola  cinerea. 

E.  Fissura  suprasylvia. 

F.  Fissura  dentata. 

G.  Corpus  callosum. 

J .  Ventriculus  tertius.  ' 

0.  Ventriculus  lateralis. 

P.  Fimbria  hippocampi. 

1.  Tractus  opticus. 

2.  Infundibulum. 

3.  Hippocampus. 

4.  Substantia  grisea  fissurae  dentatae. 
.5.  Cornu  inferius.ventrieuli  lateralis. 

6.  Lobus  hippocampi.. 

7.  Pulvinar. 

8.  Lamina  pinealis. 

9.  Columna  fornicis. 
10.  Corpus  mamillare. 
15.  Corpus  pineale. 


Fig.    2.      MAKE    THE    INCISION    ABOUT    2.5    CM. 

CEPHALAD  TO  THE  POLUS  POSTICUS, 
ending  on  the  ventral  surface  about  the  tractus  peduncu- 
laris  transversis. 

A.     Fissura  longitudinalis. 

E.     Fissura  suprasylvia. 

3.     Hippocampus. 

5.     Cornu  inferius  ventriculi  lateralis. 

6.,     Lobus  hippocampi. 

11.  Aquaiductus  cerebri. 

12.  Corpus  geniculatum  internum. 

13.  CoUieulus  superior. 

14.  Tractus  pyramidalis. 


ANATOMY   OF   THE   BRAIN 


173 


Fig.  1     ►Section  Through  the  Corpus  Pineale. 


Pig.   2— Seetion   2.5   mm.    Anterior  to   Ihe   Posterior  Ex- 
tremity of  the  Cerebrum  (x  2). 
PLATE  XXVIII. 


174  ANATOMY   OF    THE   BRAIN 


PLATE  XXIX. 

Fig.   1.       SECTION   THROUGH    THE    CRURA   AND 
COLLICULI  SUPERIORES. 

Fig.  2.       SECTION  THROUGH  THE  CRURA 

intermediate  between  the  N.  aeulomotorius  and  the  cephalic 
border  of  the  pons. 

Fig.  3.       SECTION  IMIMEDIATELY  CEPHALAD  TO 
THE  PONS. 

A.  Nu.  oenlomotorii. 

B.  Traetus  pyraniidalis  peduncnli. 

C.  Striae  longitudinales   (sections  of). 

D.  Aqiiaeductus  cerebri. 

E.  Fibrae  transversae  colliculi  superiores. 

F.  Traetus  cerebro-thalannis. 

G.  Sulcus  inter-collicuius. 
H.     Colliculus  superior. 

I.  Traetus  peduneularis  transversus. 

J.  Corpus   geniculatum  internum. 

K.  Traetus  colliculus  iuferius. 

L.  (a^     Stratum  opticum  in  fig.  2. 

(b)     Brachium  conjunctivum  in  fig.  3. 

A.  Crus. 

0.  Ventriculus  quartus. 

7*.  Colliculus  inferior. 

Q.  Nucleus  ruber. 


PLA'J'K 


XXIX-SE(ri'l<)XS    'IIIROlUilf    THE 
LICULUS  SUPERIOR  AND  (JKIKA 
CEKEBKT  fx  2  2/3). 


COL- 


176  ANATOMY   OF   THE   BRAIN 


PLATE  XXX. 

Fig.  1.     2mm.  CEPHALAD  TO  THE  CAUDAL  BOR- 
DER OF  THE  PONS. 

Fig.  2.     THROUGH  THE  N.  TRIGEMINUS. 

Fig.    3.     THROUGH  THE  CENTER  OF  THE  TRA- 
PEZIUM. 

A.  Bracliium  pontis. 

B.  Pyramis  anterior.    Fasciculus  longitudinalis  super- 
ficialis  pontis. 

C.  Stria  longitudinalis  medialis. 
L.     Brachium  conjunctivum. 

0.  Sulcus  longitudinalis  fossae  rhomboideae  ventriculi 
([uarti. 

Q.  Fibrae  pontis  superficiales  ventrales. 

E.  Raphe  pontis. 

T.  Corpus  restiforme. 

V.  Velum  medullare  anterius. 

y.  Eminentia  medialis. 

W.  Fibrae  pontis  superficiales  laterales. 

X.  Eminentia  facialis. 

y.  Vermis  cerebelli  minor. 

Z.  Nucleus  olivaris  inferior. 

5.  N.  trigeminus. 

6.  N.  abducens. 

7.  N.  facialis. 


PLATJ:    XXX-SECTIONS    THROUGH    MHE    PONS 
AND  TRAPEZIUM    (x  2  2/3). 


178  ANATOMY    OF    THE   BRAIN 


PLATE  XXXI. 

Fig.  1.     THROUGH  THE  OLIVAE. 

Fig.  2.     THROUGH  THE  N.  ACUSTICUS. 

Fig.  3.     THROUGH  THE  CAUDAL  THIRD  OF  THE 
THE  VENTRICULUS  QUARTUS. 

B.  Pyramis. 

C:  Stria  longitudinalis  profundis. 

F.  Sulcus  limitans  fossae  rhomboideae. 

/.  Eminentia  medialis. 

0.  Sulcus  longitudinalis  fossae  rhomboideae. 

F.  Area  acustica. 

Q.  Ventriculus  quartus. 

U.  Raphe. 

T.  Corpus  restiforme. 

Z.  Oliva  (nucleus  of). 

5.  Radix  aseendens  N.  trigemini. 

8.  N.  acusticus. 


anato:my  of  the  brain 


17  9 


PLATK  XXXI-.SECI10N8  THROUGH  THE  MEDUL- 
LA OBLONGATA   (x  2  2/3). 


180  ANATOMY   OF   THE   BRAIN 


PLATE  XXXII. 

Fig.  1.   SECTION  THROUGH  THE  CAUDAL  FOURTH 
OF  THE  VENTRICULUS  QUARTUS. 

Fig.   2.      SECTION  AT  THE  ENTRANCE  OF  THE 
CANALIS  CENTRALIS. 

Fig.   3.     SECTION  THROUGH  THE  CAUDAL  BOR- 
DER OF  THE  OBEX. 

Fig.  4.     SECTION  OF  MEDULLA  SPINALIS. 
B.     Pyramis. 
D.     Columna  dorsalis. 
G.     Substantia  gelatinosa. 

11.  Columna  ventralis. 
J.      Canalis  centralis. 

K.  Substantia  gelatinosa  centralis. 

L.  Fissura  ventralis. 

B.  Raphe. 

T.  Corpus  restiforine. 

X.  Obex. 

5.  Radix  ascendens  N.  trigemini. 

7.  Sulcus  dorsalis. 

12.  Eminentia  hypoglossi. 


J>LATE   XXXIT-SKCTTONS   THROUGH   THE  MKD- 

ULLA  OBLONGATA  AND  SPINAL 

COKD   (x  2  2/3). 


182  ANATOMY    OF    THE   BRAIN 


PLATE  XXXIII.  : 

ENLARGED   SECTION  OF   THE   MEDULLA 
SPINALIS. 

A.  Fissura  ventralis. 

B.  Funiculus  ventralis. 

C.  Sulcus  ventralis  lateralis. 

D.  Columna  lateralis. 

E.  Funiculus  lateralis. 

F.  Fasciculus  lateralis  minor. 

G.  Processus  reticularis. 
H.  Fasciculi  longitudinales  dorsales. 
I.  Fasciculus  cerebellospinaiis. 
J.  Sulcus  lateralis  dorsalis. 
K.  Substantia  gelatinosa. 
L.  Fasciculus  cuneatus. 
M.  Sulcus  intennedius  dorsalis. 
N.  Fasciculus  gracilis. 
0.  Sulcus  dorsalis. 
P.  Fasciculus  fusiformis.- 
Q.  Commissura  dorsalis. 
R.  Columna  dorsalis. 
8.  Radix  dorsalis  nervi  spinalis. 
T.  Canalis  centralis. 
U.  Commissura  ventralis  grisea. 
V.  Fasciculus    intereommissuralis    ( Dexel    & 

Margulies)    ventralis. 

W.  Radix  spinalis  N.  accessorii. 

X.  Commissura  ventralis  alba. 

Y.  Columna  ventralis. 

Z.  Radix  ventralis  nervi  spinalis. 


ANATOMY    OF    THE    BKAIN 


183 


<?X 


PLATE  xxxiii-enlargp:d  section  of  spinal 

CORD  .5  CM.,  CAUDAD  TO  MEDULLA 
OBLONGATA. 


184  ANATOMY   OP   THE   BRAIN 


PLATE  XXXIV. 

SECTION    THROUGH    THE    LOWER    PORTION    OF 
THE  MEDULLA  OBLONGATA,  SHOWING 
THE  DECUSSATION  OF  THE  PYRA- 
MIDAL FIBRES. 

A.  Fissura  ventralis, 

B.  Pyramis, 

C.  Pyramis,  decussation  of, 

D.  Fasciculi  longituclinales  dorsales, 

E.  Fasciculus  cuneatus, 

F.  Fasciculus  Gracilis, 

G.  Fasciculus   fusiformis, 

H.  Radix  dorsalis  N.  spinales, 

I.    Substantia  gelatinosa    (Rolando),  • 

J.    Fasciculus   cerebellospinalis, 

K.  Forraatio  reticularis, 

L.  N.  hypoglossus  (caudal  extremity), 

0.  Fasciculus  lateralis  minor, 


ANATOMY  OF   THE  BRAIN 


185 


A    B 

PLATE    XXXIV. 


186  ANATOMY  OP  THE  BRAIN 


PLATE  XXXV. 

SECTION   THROUGH   THE   NUCLEI   ARCUAT.T. 

A.  Sulcus  ventral  is. 

B.  Pyramis. 

C.  Nuclei  arcuati. 
X>,  N.  hypogiossus. 

E.  Fasciculus  lateralis  minor. 

F.  Fibrae  arcuatae  externae. 

G.  N.  Glossopharyngi. 
H.  Corpus  restiforme. 
./.  Nucleus  cuneatus. 

J.  Nucleus  gracilis. 

K.  Fasciculus  fusiformis. 

L.  Nucleus  hypogiossus. 

M.  Taenia  ventriculi  quarti. 

N.  Ventriculus  quartus. 

0.  Ramus  obiseis. 

P.  Nucleus  glossopharyngeus. 

Q.  Fasciculus  solitarius. 

B.  N.  vagus.  ' 

S.  Tractus  spinalis  N.  trigcmini. 

T.  Nucleus  tractus  spinalis  N.  trigeiiiini. 

JJ.  Formatio  reticularis  grisea. 

y.  Formatio  reticularis  alba. 


akatomy  of  the  brain 


187 


188  ANATOMY  OF  THE  BRAIN 


PLATE  XXXVI. 

SECTION  THROUGH  THE  CAUDAL  THIRD  OF  THE 
FOURTH  VENTRICLE. 

A.  Pyramis  ventralis. 

B.  Lemniscus  meclialis. 

C.  Fasciculus  lateralis  minor    (Gower). 

D.  Tractus  spinalis  N.  tragemini. 

E.  Corpus   restiforme. 

F.  Nucleus  vagi,  dorsal  and  ventral  areas. 

G.  Plexus  ehorioideus  ventriculi  quarti. 
H.  Taenia  ventriculi  quarti. 

/.  Tractus  solitarius  N.  vagi. 

J.      Nervus  vagus. 

K.  Fibrge  arcuatce  externa?. 

L.  Eminentia  medialis. 

M.  Nucleus  ambiguus  N.  vagi. 

N.  Fibras  arcuatae  internae. 


ANATOMY   OF   THE   BRAIX 


189 


190  ANATOMY  OF  THE  BRAIN 


PLATE   XXXVII.  ;: 

SECTION  THROUGH  THE  TRAPEZIUM,  COCHLEAR 
AND  VESTIBULAR  NUCLEI. 

A.  N.  coehl*. 

B.  Nucleus  dorsalis  N.   eochlearis. 

C.  Striae  niedul lares. 

D.  Nucleus  ventral  is  N.  eochlearis. 

E.  Corpus   restifonne. 

F.  Fibres  from  the  nucleus  ventral  is  N.  eochlearis. 

G.  Fibres  from  the  nucleus  dorsalis  N.  eochlearis. 
H.  Nervous   vestibuli. 

7.  Nucleus  lateralus  N.  vestibuli   (Deiter). 

/.  Radix  descendens  N.  vestibuli. 

K.  Nucleus  oliva:\ 

L.  Nucleus  N.   facialis. 

M.  Pars  prima  N.   facialis. 

N:  Nucleus  N.   abducentis. 

0.  Genu  N.  facialis. 

P.  Fibres  of  the  trapezium. 

Q.  Nucleus  tractus  spinalis  N.  trigemini. 

R.  Tractus  spinalis  N.  trigemini. 

S.  Tractus  pyramidalis. 

T.  N.  abducens. 

v.  Fibrfp   arcuata^  externae. 

V.  Decussation  of  the  stritv  medulla  res  from  the  dorsal 
and  ventral  cochlear  nuclei. 

W.  Formatio  reticularis. 

X.  Fasciculus  lateralis  minor. 

¥.  Nucleus  dorsalis  N.  vestibuli.  ^ 

Z.  Area  aeustica. 


ANATOMY  OP   THE  BRAIN 


191 


.  my 


CM 

192  ANATOMY  OF  THE  BRAIN 


PLATE  XXXVIII. 

SECTION      THROUGH      THE      COLLICULI      SUPE- 

RIORES. 

A.  N.   oculomotor-ins,   fibres  leading  from   its   nncleus. 

B.  Pyramis. 

C.  Corpus  genicnlatus  externum. 

D.  Stratum  opticum. 

E.  Colliculus  superior. 

F.  Stratum  griseum  eentrale. 

G.  Corpus   geniculatum  internum. 
H.  Aquaeduetus  cerebri. 

/.      Nucleus  ruber. 

J.      Fasciculus  retroflexus   (Meynert). 

L.     Lamina  quadrigemina. 


ANATOMY   OF   THE   BRAIN 


193 


PLATE  XXXVIII-SECTION  THROUGH  THE  COLLICULI 

^;:'^    ''?:!! '  SUPERIOKES. 


194  ANATOMY  OF  THE  BRAIN 


PLATE  XXXIX. 


THE  BASE  OF  THE  SKULL 
with  the  dura  mater  and  the  nervi  cerebrales  in  position. 


1. 

N.  olfaetorius. 

2. 

Tractus  opticus. 

3. 

N.  oculomotorius. 

4. 

N.  pathetieus. 

5. 

N.  trigeminus. 

6. 

N.  abdueens. 

7. 

N.  facialis. 

8. 

N.  acusticus. 

9. 

N.  Glosso-pharyngeus. 

10. 

N.  vagus. 

11. 

N.  accessorius. 

12. 

N.  hypoglossus. 

AA 

.  Sinus  frontales. 

B. 

Crista  galli. 

C. 

Fossa  olfactoria. 

D. 

Fossa  frontalis. 

E. 

Foramen  opticum. 

F. 

Commissura  optica. 

G. 

Recessus  infundibuli. 

H. 

Infundibulum. 

I. 

Foramen  diaphragmatis  sellae. 

J. 

Arteria  carotis  interna. 

K. 

Fossa  hippocampi. 

L. 

Tentorium  cerebelli. 

M. 

Foramen  magnum. 

N. 

Meatus  acusticus  internus. 

P. 

Foramen  jugulare. 

R. 

Dura  mater. 

S. 

Fossa  parietalis. 

T. 

Condylus  occipitalis. 

ANATOMY   OF  THE  BRAIN 


195 


1^1   \TF  XXXJX-HASE  OF  SKULL  SHOWING  DURA 

MA'['FAi  AVITII  EXITS  OF  CRANIAL 

NERVES  (X  1  1/3). 


196  ANATOMY  OF  THE  BRAIN 


PLATE  XL. 

BASIS  CRANII. 

A.  Sinus  frontales. 

B.  Lamina  cribrosa. 

C.  Crista  galli. 

D.  Sulcus  chiasmatis. 

E.  Fissura  sphenoidalis. 

F.  Processus  clinoideus  anterior. 

G.  Fossa  hypophyseos  (sella  turcica), 
H.  Sulcus  caroticus. 

/.  Foramen  ovale. 

J.  Processus  clinoideus  posterior. 

K.  Fossa  jugularis. 

L.  Dorsum  sellae. 

M.  Sulcus  sigmoideus. 

N.  Meatus  acusticus  internus. 

0.  Condylus  occipitalis. 

P.  Foramen  eondyloideum. 

B.  Foramen  occipitale  magnum. 

S.  Pars  petrosa. 

T.  Os  basilare. 


ANATOMY  OF   TJIE   BRAIN 


197 


PLATK   XI-.     IJASi:   Ol-'  1'1IH   SKUl.l.    (x   T   l/:i}. 


INDEX . 


Ala  ciiRTca,  !)(>,   Ill 
Anterior  cerebellar  artery,  29,   12o 
Anterior  cerebral  artery,   28,    12o 
Anterior  column  of  spinal  conl    ( tiiiiicii 

Ins  ventralis),    185 
Anterior  commissure,   4.'5.   51,   77.    155 
Anterior   coininiinicating   artery,   30 
Anterior  liinb  of  internal  capsule,  72,  153 
Anterior  perforated  space,  44 
Anterior  spinal  artery,  30 
Anterior  pillars  of  fornix,   78 
Antero-lateral  fissure,  97 
Aperatura  mediana  ventriculi  ciuarti,  27, 

52,  94 
A<iufeduetus   cerebri,   53,    103 
Aqueduct  of  Sjdvius,  53 
Araclinoidea   encephali,   24 
Arachnoid   membrane,    24 
Arbor  vit*.  54,   133 
Area  acustica,  91,  103,  167 
Area  lateralis  thalami,  72,    153 
Area  medialis  thalami,  72,    153 
Area  posterior  thalaiui,  72,   153 
Area  postrenia  of  Retzius,    112 
Arteria  basilaris,  29,   125 
Arteria  basilaris  gaiigliforniis    postcriijr, 

29,  125 
Arteria  carotis  interna,  28 
Arteria   cerebelli   anteiior,   29,    125 
Arteria  cerebelli  postericn',  29,  125 
Arteria  cerebri   anterior,   28,    125 
Arteria  cerebri   media,  29,   125 
Arteria  cerebri   ])osterior,  29,   125 
Arteria   propria   cerebri,    28,    125 
Arteria   spinalis   ventralis.   30 
Arteria;  communicantes  fndi'rioKs,   30 
Arteria;  meningese,  19 
Arteriic  vertebra  les,  30 
Ascending  [)art   (N".  facialis),  92 
Associiitioii    bundles,    (»0 
Aula,    80 
Axoncs,  31 


Pmsiiar    artery,    30 

Basis   cranii,  22,    197 

Btchterew's  nucleus,  92 

Blood  vessels,  28,  125 

Bracliia  pontis,  87,  165,  167 

Bracliium  conjunctivae,  86,   167 

Bracluum    quadrigeniiiiii    iiiferius,    83, 

104,    159 
Broca's  limbic  fissure,  50 
Broca's  quadrilateral   space,   44 
Bulbe   rachidian,  93 
Bnlbi   fornicis,  45,    131 
Bulbi  olfactorii,   17,  43,   131 
Burdach's  tract,  107 
Calamus  scriptorius,   112 
Canalis  centralis,  54,   183 
Capsula  externa,  52,  72,  153 
Capsula  interna,  71,   153 
Caput  nuclei  caudati,  61,  143 
Caudate  nucleus,  63 
Cavum  septi  pellucidi,  62 
Cavum  subaraehnoideale,  24 
Cavum  subdurale,  24 
Cell  staining,  31 

Central  canal  of  spinal  cord,  110,  183 
Cerebellar  bridge   (pons),  87 
Cerebellar  peduncles,  inferior,  102 
Cerebellar  peduncles,  middle,  87 
Cerebellar  penduncles,  superior,  86 
Cerebellar  arteries,  anterior,  29 
Cerebellar  arteries,  posterior,  29 
Cerebellar  licinis|)li('res,  39,   127 
< 'crebelluin,    15 

Ciichral  arteries,  anterior,  28 
(crchral   a r1  cries,   middle,  29 
(  rrcbiai  arteries,  posterior,  29 
Cerebral   convolutions,  32 
('eicbral    ])eduneles,  94,   131 
Cerebral    ])r<.t  ni.eiance  of  (Joll,   93 
Cei'ebrnMi,    15 
(  liiasma,  oj)! iciiin,  44.   131 
Cinguluni,  57 


200 


ANATOMY  OF  THE  BRAIN 


Cingulum  inferius,   58 

Cingulum  super ius,  57 

Circle  of  Willis,  30 

Circulation  at  the  base  of  the  brain,  30 

Circulus  arteriosus,  30 

Cisterna  subarachnoidea,  24 

Clava,   103,   167 

Claustrum,  72,   153 

Colliculus  facialis,  167 

Colliculus  inferior,  82,  167 

Colliculus  superior,  71;  146.  193 

Columna  dorsalis,  183 

Columna  lateralis,   183 

Columna  ventralis,  97,  183 

Columnae  fornicis   anteriores,   61,    147 

Columnse  fornicis  posteriores,  65,   149 

Commissura  anterior,  43,  51,  77,   155 

Commissura  anterior   (dissection  of),  77 

Commissura  dorsalis,  183 

Commissiira  liabenulariun,  75 

Commissura  hij^pocampi,   65 

Commissura  medialis,  54,  133 

Commissura  posterior,  53,  133 

Commissura  optica,  44,   131 

Commissura  ventralis  alba,  183 

Commissura  ventralis  grisea,  183 

Conarium,   75 

Conchfe  ethmoideales,   16 

Condyli  occipitales,  16,  197 

Confluens  sinuum,  21 

Cornu  anterius  ventriculi  lateralis,  02 

Cornu  inferius  ventriculi  lateralis,  57, 

62,  143 
Cornu  posterior  ventriculi  lateralis,  57 
Cornua,   62 

Corona  radiata,  85,  161 
Corpora  albicantia,  45,   131 
Corpora  mamillaria,  45,  131 
Corpora  quadrigemina,  53,  69,  82 
Corpus  callosum,  49,  133,  137,  139 
Corpus  fimbriatum,  65 
Corpus  fornicis,  61,  65,  149 
Corpus  geniculatum  externum,  71,  193 
Corpus  geniculatum  intei'num,  71,   193 
Corpus  medullare  cercbelli,  38,  54,  133 
Corpus  pineale,  53,  75,  133,  147 
Corpus  restiforme,  90,  100,  187,   189 


Corpus  striatum,  44 

Corpus  trapezoideum,  90 

Cortex,  31 

Corticifugal  fibres,  60 

Corticipetal  fibres,  60 

Crista  galli,  197 

Crura   cerebri,   45 

Crura  fornicis  posterior,   65 

Crus  cerebelli   ad  corpora  quadriguniiii 

103 
Decussation  of  the  Nn.  trochlear.'s.  95 
Decussation  of  the  pyramids,  97,  U'5 
Deiter's  nucleus,  92 
Dentate  fassia,  57 
Dentate  fissure,  67 
Depressio  interfusiformis,  1(57 
Diacoele,  80 

Direct  cerebellar  tract,   102 
Dissecting  Wax,  12 
Dorsum  sellse,  197 
Dura  mater  encephali,    19,    123 
Eminentia  facialis.   90.   ]  1 1 
Eminentia  hj'poglossi.  Ill 
Eminentia  medialis,  89,    110,    167,    187 
Eminentia  teres    (facialis),  90 
Eminentia  vagi,  96 
Encephalon,  15 
Ependyma,   39 
Ejjineurium,   22 
Epiphysis,  75 

Espace  quadrilatiere  of  15rt:ca.  44 
Ethmoturbinals.    16 
External  capsule,   72 
External  geniculated  body.   71 
Facies  dorsalis  cerebelli,  38.   127 
Faeies  lateralis  cerebelli,  39 
Facies  medialis  cerebelli,   51,   133 
Facies  dorsalis  cerebri,  33,   127 
Facies  lateralis  cerebri,  41,  129 
Facies  medialis  cerebri,  49.  133,  157 
Facies  ventralis  cerebri,  43,   131 
Falx  cerebri,  20 
Fascia  dentata,  57,  62 
Fasoia  dentata  hippocampi,  68.  151 
Fasciculi   longitiulinales   dorsales,  98, 

183 
Fasciculus   cerebellospiiialis,    100.    183 


ANATOMY   OF   THE  BRAIN 


201 


Fa-icicuhis  ciineatiis,    102.   107,   183 
Fasciciilus  fiisiformis,   106,  167,   183 
Fasciculus  gracilis,    107,    183 
Fasciculus  lateralis  minor,  98,   183,    183, 

187,    189,    191 
Fasciculus   longitudinalis   nu'dialis,   88 
Fasciculus   longitudiiialis   proliunlis   pon- 

tis,  88,   177 
Fasciculus      longitudiiialis      suiuMticialis 

pontis,  87 
Fasciculus  retrofle.ws,  73,   193 
Fasciculus  separans,  112 
Fasciculus  subcallosus,  58,   149 
Fasciculus  tlialamomaniillaris,  79,   137 
Fasciculus    ventralis    intracoramissuralis 

[longitudinalis]    (Dtxid  &   Maigulies  ) . 

182 
Fasciculus     ventrolatoalis     su[)crficialis. 

99 
Fasciola  cinerea,  53,  68,   133 
Fibrse  arcuatai  externip,  100,  187 
Fibrae  arcuatie  intern.T,   189 
Fibrse   longitudinales,    85 
Fibrae  pontis  profunda'.  88,   177 
Fibrae  pontis  superficialos,  84 
Fibrae     transversae     colliculi     suijcriores, 

175 
Fifth  ventricle,   62 
Fillet,   108 

Fimbria   hi]>pocamj)i.    62,    149,    173 
Fissura  cerebelli   medialis,   127 
Fissura  cerebelli  inferior,  127 
Fissura  cerel)elli  superior,  127 
Fissura  cerebri  lateralis,  41,  129 
Fissura   cerebri   intermedia   dorsalis 

(sulcus),  127 
Fissura    cerebri    lalcialis    dorsalis 

(sulcus),   127 
Fissura   cerebri    iiifdialis   dorsalis 

(sulcus),  127 
Fissura  coionalis    (-ulcus),  33 
Kissura  cniciata,  33,  127 
Fissura  dentata,  67,   151 
Fissura  hippocampi,  68 
Fissura  limbica,  of  IJroca,  30 
Fissura  liird)icii,  of  Tiirnei-,  41 


Fissura  longitudinalis  cerebri,  20,  31, 
127 

Fissura  inediaiia  dorsalis  medullae  spin- 
alis, 97 

Fissura  mediana  ventralis  medullae  ob- 
longatae,  96 

Fissura  rhinalis,  41,  130 

Fissura  sagittalis,   130 

Fissura  sphenoidalis,  22,  197 

Fissura  suprasylvia,  33,   127 

Fissura  transversa  ct-rebri.  20.  :!3.  67 

Fissura  venti^alis,  183 

FissunB   lerebelli,   39,    133 

Fissure  of  Sylvius,  41 

Flocculus,  40,  88,  129 

Floor,  of  ventriculus  teitius,  53 

Folia  cerebelli,  38 

Foramina  condyli   anteriora,  21 

Foramen  condyloideum,  197 

Foramen   diaphragmatis  sella'.   28 

Foramen  jugulare,  22 

Foramen   interventriculaic,   (>'.).   145 

I'^oramen  of  Magendi,  27,  94 

Foramen  of  Monroe,  63 

I'inamen  oeciiiitale  maginim.    16 

Foramen  optieum,  195 

Foramen  ovale,  194 

Forceps  anterior,  37 

J'\)rceps,  major,  57 

Forceps,  minor,  57 

Forceps  posterior,  57 

Formatio  reticularis  alba,   108,   187 

Formatio  reticularis   grisca,    187 

Fornix.  65.    143,   149 

Fossa  cranii   anterior,   194 

Fossa  cranii   media,  22 

Fossa  cranii   poslciior,    197 

Fossa  frontalis,   194 

]"'ossa   liippociunpi,  194 

l''ossa    by|)0]i]iyse()s,  28,    194 

Fossa  interpeduiiciilaris,  24,   45 

Fossa  olfactoria,  194 

Fossa  orbital  lis,  15 

Fcssa  parielalis,    19  1 

Fo.s.sa  rlioiiilMiidca.  1 10.  106 

Fossa    suhpiiicalis,   75 


202 


ANATOMY  OF  THE  BRAIN 


Fossa  temporalis,  22 

Fovea  anterior,   111,   167 

Fovea  posterior,   111,   167 

Frontal  siniLses,   15,  197 

Funiculus  lateralis,  102,  183 

Funiculus  ventralis,  183 

Galen,  rete  mirabile,  22 

Galen,  vein  of,  20 

Ganglion  liabenulse,   75 

Ganglion  semilunare    (Gasser),  22 

Gasserian  ganglion,  22 

Genu  capsulfe  internse,  71,  153 

Genu  corporis  callosi,  49,  133 

Genu  nervi  facialis,  92,   191 

Globus   pallidus,   72 

GoU's  cerebral  protuberance,  93 

Goll's  tract,   107 

Gower's  tract,  99 

Great  commissure,  56 

Great  longitudinal  fissure,  31 

Great  tranverse  fissure,  33 

Gyri  centrales,   129 

Gyri  cerebri,  32 

Gyri  mediales,   127 

Gyrus  arcuatus,  42 

Gyrus  cinguli,  50,  133 

Gyrus  dentatus,  57 

Gyrus  fornicatus,  50 

Gyrus  frontalis  inferior,  42,  129 

Gyrus  frontalis  medialis,  33 

Gyrus  frontalis  superior,  33,  127 

Gyrus  intermedins,  50,  133 

Gyrus  internus,  127 

Gyrus  lateralis,  127 

Gyrus  marginalis  anterior,  51,  133 

Gyrus  marginalis  posterior,  50,  133 

Gyrus  orbitalis,  42,  129 

Gyrus  parietalis  externalis,  34 

Gyrus  parietalis  internalis,  34 

Gyrus  parietalis  medialis.  34 

Gyrus  rectus,  44 

Gyrus  sylviacus,  41 

Hebenulfe,  75 

Hemisplieria  cerebelli,  39,  127 

Hemisphserium  cerebri,  31 

Hippocampus,   59,   61,   67,   143 


Hypophysis,  44,   155 

Inferior  cerebellar  peduncle,   102 

Inferior  frontal  gyrus,  42 

Infundibulum,  44,  53,  131 

Insula,   41,    129 

Internal  capsule,  71 

Internal  carotid  artery,   28 

Internal  geniculated  body,  71 

Internal  parietal  gyrus,  34 

Interpeduncular  nucleus,  34 

Interpeduncular  space,  24 

Island  of  Reil,  41,  129 

Iter    a   tertio    ad   quartum    ventriculuiu. 

53 
Kaiserling  method,  73 
Lambdoid   suture,    16 
Lamina  cinerea,  52  .  .  , 

Lamina  cribrosa,   197 
Lamina  pinealis,  53  . 

Lamina  quadrigemina,  55,  133,  193 
Lamina  rostralis,  52 
Lamina  terminalis,  51,  52 
Lancisi,  nerves  of,  56 
Lateral  column  of  the  spinal  cord,   182. 
Lateral  sinus,  17 
Lateral  ventricule,  56 
Lemniscus  lateralis,  83 
Lemniscus  medialis,   108 
Lenticular  nucleus,   72 
Ligamentum  denticulatum,  27,   163 
LigTila,  95 

Limbic  fissure  of  Broca,  50 
Limbic  fissure  of  Turner,  41 
Lissencephala,  50 
Lobi  cerebelli,   39,   133 
Lobi  cerebri,  32 
Lobus  cerebelli  inferior,  39,  129 
Lobus  cerebelli  medialis,  39,   129 
Lobus  cerebelli  superior,  39,  129 
Lobus  centralis,  41,    129 
Lobus  frontalis,  34 
Lobus  hippocampi,  43,  131 
Lobus  occipitalis,  33 
Lobus  parietalis,  34 
Lobus  superior,  cerebelli,  39,  127 
Lobus   temporalis,   34 


ANATOMY   OF   THE   BRAIN 


•203 


Locus   inleipfduuculaiis,   80 

Locus  perforatiLs  anterior,  44,  131 

Locus    perforatus   posterior,   45 

lx)ngitudinal  sinus,   17 

Magendi,  foramen  of,  27 

^largo  corporis  fornicis,  145 

Massa  intermedia,  132 

Meatus  acusticus  interna,  ]!Hi 

Medulla  oblongata.    15,  47.  !>3,   163,   185, 

187.   189. 
Medulla  spinalis,  47 
^feningeal  arteries,   1!) 
Meninges,  17 

Meynert's   facieulus,  75.   103 
Middle  cerebellar  peduncle.  87.  103 
Middle  cerebral  artery,  29 
Middle  commissure.   132 
Monroo,  foramen  of.   02 
Motor  fasciculus,  5th  nerve,   152 
Motor  areas,  35,  36 
Xates,  82 

Xenes  of  Lancissi,  oi) 
Xervi  abducentes,  46,  131,  191 
Xervi  accessorii,  27,  47,  131 

Xervi  acustici,  46,  131.  191 

Xervi  cerebrales,  17 

Xervi  faciales,  46,  131.   191 

Xervi  glossopharyngei.  47,   131 

Xervi  hypoglossi,  47,  131.  185 

Xervi  oculomotoiii,  45 

Xervi  olfactorii,  45,  131,  193 

Xervi  optici,   17,  44,   131, 

Xervi  pathetici,  45 

Nervi  spinales,  47 

Nervi  trigemini,  45,   131,   177,   179,   187, 
189 

Xervi  trochlearc.s,  45,  131 

Xervi  vagi,  47,  131 

Nervus  cochlearis,  91 

Xervus  mandibularis,  22 

Xervus  maxillaris.  22 

Xervus  ophthalmicus,  22 

Nervus  vestibularis,  91 

Neurones,  31 

Nuclei  arcuati,  101,  187 

Nuclei  pontis,  87 

Nucleus  abdueenlis,  92,  19] 


Nucleus  ala;  cinerete,  112 

Xucleus  ambiguus,  112,  189 

Xucleus  caudatus,  63 

Xucleus  cuneatus,  108,  187 

Xucleus  dorsalis  X.  cochlearis,  91,  191 

Nucleus  doi-salis  N.  vestibularis,  91 

Nucleus  facialis,  90,  92,  108.  191 

Xucleus   fasciculus   fusiformis,    108 

Xucleus   glosso-pharyngeus,    112,    187 

Xucleus  gracilis,   108,   187 

Nucleus  interpeduneularis,  45,   131 

Xucleus   lenticularis,   72,    153 

Xucleus  lentiformis,  72,  153 

Xucleiis  Xervus  Acstibularis.  91 

Xucleus  olivaris  inferior,  92,   191 

Xucleus  ruber,   85,    193 

Nucleus  tractus   spinalis   X.  trigemini, 

112,  190 
Nucleus  vagus,   112.   189 
Nucleus  ventralis  N.  cochh'nris,  91,    191 
Obex,  106,  167 

Olfactory  bulbs,  43 

Olfactory  tracts,  43 

Oliva,  99,  163 

Operculum,  42 

Optic  chiasm,  44 

( )])tic  conunissiu'e,  44 

Optic  nerve,   17 

Optic  thalamus,  70,  147 

Optic  tracts,   44.    131 

Orbital  fossae,   15,   121 

Os  basilare,  21,   197 

Os  occipitale,  21 

Os  parietale,  34 

Os  sphenoidale,  22 

Os  temporalis,  22 

Ossa   cranii,    15 

Pallium,  31 

I'araflocculus,  40,   129 

Par  vagum,  47 

Pars  centralis  thalami,  72,  153 

Pars  frontalis  ca])sulifi  interna',  72,  153 

Pars  libra  columna?  fornicis,  78 

Pars  petrosa  ossis  temporalis,  22,  197 

Pars  posticus  capsula;  interna,  72,  153 

Pars  prima  N.  facialis,  92,  191 

Pars  secunda  N.  facialis,  92,  177 


204 


ANATOMY  OF  THE  BRAIN 


Pars  tecta  columnse  fornicis,  51,  78,   157 

Pedunculi  cerebri,  45,  131 

Pia  mater  encephali,  26 

Pigment  granules,  26 

Pineal  gland,  75 

Pituitary  body,  44,  155 

Plexus    chorioideus    ventriculi    lateralis, 

61,  143 
Plexus  chorioideus  ventriculi  quarti,  94. 

95,  108,  189 
Plexus   chorioideus   ventriculi   tertii,   59. 

64,  69,  145 
Pneumogastric  nerve,  47 
Polus  anticus,  33 
Polus  frontalis,  41 
Polus  occipitalis  cerebri,  65 
Polus  posticus,  34 
Pons,  15,  45 
Pons  Tarini,  45 
Pons  Varolii,  45 
Pontal  nuclei,  87 
Porta,  63 

Portio  dura  of  Willis,  90 
Portio  mollis  of  Willis,  90 
Portio  motor  aST.  trigemini,   152 
Posterior  cerebellar  artery,  29 
Posterior  cerebral  artery,  29 
Posterior  commissure,  133 
Posterior  limb  of  internal  capsule,  72. 

153 
Posterior  longitudinal  bundle,  110 
Posterior  perforated  space,  45 
Posterior  pillars  of  the  fornix,  65 
Postro-external  tract    (Goll),   107 
Postro-internal  tract    (Burdach),   107 
Principal  vestibular  nucleus,  91 
Processus  clinoideus  anterior,  197 
Processus  clinoideus  posterior,   197 
Processus  reticularis,  97,  183 
Protuberantia  occipitalis  externa,  21 
Pseudocoele,  62 
Pulvinar,  70,  147 
Putamen,  72,  153 
Pyramidales,  87 
Pyramis,  N.,  97,   179,   185,  187 
Pyramis  ventralis,  85,  189 
Rachidian  bulb,  93 


iladiatio    corporis    callosi,    57 
Piadicular  part.    (N.  facialis),  92,  99 
Radix  ascendens  N.   trigemini,   90,  99, 

179 
Radix  cerebralis  N.  accessorius,  47 
Radix  descendens  N.  vestibularis,  91, 

191 
Radix  dorsalis  nervi  spinales,  182 
Radix  intermedia  bulbi  olfactorii,  43, 

131 
Radix  lateralis  bulbi  olfactorii,  43,  131 
Radix  medialis  bulbi  olfactorii,  43,  131 
Radix  spinalis  nervi  accessorii,  182 
Radix  ventralis  nervi  spinalis,  182 
Rami  obicis,  110,  111 
Ramus  anterior  arterise  proprise,  28,  125 
Ramus  anterior  fissurae  lateralis  cerebri, 

41,  129 
Ramus  posterior  arterije  propriae,  28, 

125 
RamvLs    posterior    fissurae    lateralis    cere- 
bri, 41,  129 
Raphe  corporis  callosi,  56 
Raphe  pontis,  88 
Recessus  infundibuli,  53 
Recessus  lateralis  ventriculi  quarti,  81 
Recessus  opticus  ventriculi  tertii,  53 
Recessus  pinealis  ventriculi  tertii,  76 
Recessus  triangularis,   143 
Reil,  Island  of,  41 
Rete  mirabile  of  Galen,  22,  28 
Retzius,  area  postrema  of,   112 
Rostrum  corporis  callosi,  49,   133 
Schneiderial  membrane,  16 
Sella  turcica,  44 

Sensory  fasciculus,  fifth  nerve,  163 
Septum  pellucidum,   61,   145 
Sinus  basilaris  magna,  21 
Sinus  cavernosus,  22 
Sinus  circularis,  22 
Sinus  frontalis,   197 
Sinus  petrosus  inferior,  22 
Sinus  sagittalis,  20,  123 
Sinus  sagittalis  superior,  17,  123 
Sinus  transversus,  17,  123 
Smooth-brained  animals,  50 
Spinal  accessory  nerve,  47 


ANATOMY  OF   THE  BRAIN 


205 


Spinal  cord,  Plate   XXXIII,   183 

Spinal  nerves,  47 

Splenii\ni  corporis  callosi,  49,   l;33 

Staining,  substantia  grisea,  31 

Stratum  cineneum,  82 

Stratum  griseum   cent  rale,    192 

Stratum  leninisei,  82 

Stratum  opticum,  82^  193 

Stratum  zonale,  83 

Stria  longitudinalis  lateralis,  oO 

Stria  longitudinalis  profiuuiis.    110 

Stria  terniinalis,  09 

Striae  aeusticae,  91 

StriiK  longitudinales,   175 

Striae   longitudinalis   mediales,   ofi 

Striae  medullares,  91.  191 

Striae  medullares  thalanii.  7ii.   7ii.    147 

Subarachnoid  space,  24 

Subdural  space,  24 

Substantia  alba,  31 

Substantia   alba  insula',    ].)3 

Substantia  intermedia,  132 

Substantia  gelatinosa,   182 

Substantia  gelatinosa   centralis,    182 

Substantia   grisea,   31,   53 

Substantia  grisea   fissnrae  dentatae.   173 

Substantia  grisea  insulae.  153 

Substantia   nigra,    85 

Substantia  perforata   anterior.   44 

Substantia    perforata    po-^teriii)-.    -15 

Sulci  cerebri,   32 

Sulci   olfactorii,    41 

Sulci  rhinales,  41 

Sulcus  basilaris,  87,   1(13 

Sulcus   caroticus,   21,    197 

Sulcus  cliiasniatis.   197 

Sulcus  cinguli,  59,  133 

Sulcus   foronalis,   33,   127 

Sulcus  corporis  callosi,  5(».   133 

Sulcus   dorsalis,    106,   167 

Sulcus  fusiformis,   167 

Sulcus    intorcollicularis,    107 

Sulcus    inler-colliculus    superior,    83 

Sulcus    intermedius,    34,    127 

Sulcu.s  intermedins  dorsalis.   107,   lii7 

Sulcus    lati-ralis,    34,    127 


Sulcus   lateralis   dorsalis,   102,    185 

Sulcus  lateralis  ventralis,  102,  185 

Sulcus  limitans  fossae  rhomboideae,  110, 
167 

Stilcus  longitudinalis  fossae  rhomboideae, 
89,  91,   110,   1G7 

Sulcus   medialis,    34,    127 

Sulcus    oculomotorius,    84 

Sulcus   olfactorius,   41 

Sulcus  parolfactorius,  51,    133 

Sulcus  semilunaris,   110,  1(57 

Sulcus    sigmoideus,    197 

Sulcus   splenialis,   33,   50,    133 

Sulcus   transversus,    112 

Sulcus    ventralis,    1()3 

Sulcus  ventralis  lateralis,  97,   103 

Sulcus  ventralis  mednlhe  oblongatae,   10? 

Superior  cerebellar  peduncle,  88,   103 

Superior   longitudinalis    sinus,    20 

Sujjerior    medullary    velum,    54 

Sntnra  coronalis,  34 

Sutura    lambdoidea,    l!i 

Sutura    sagittalis,    19 

Sylvius,  aquaduct  of.   53 

Sylvius,    fissure    of,    41 

Tapetum,  57 

Tarini,  pons,  45 

Taenia  hippocampi,   02.   05 

Taenia  seraicircnlaris,  09 

Taeniae  tcctae  (striii^  longitudinales  later- 
ales),  50 

Taenia  ventricnli  i|uai(i.    112 

Tapetum,  57 

Tegmentum   ventricuJi    rpiarti,   54 

'I'ela  chrioidcM  \cnliiculi  ipiarti.  95.  110, 
189 

T(da  chorioidea   \riiiriculi  tertii,  04 

Tentorium  cerelM'Jli.  20 

'I'estes,  82 

Thalamus   opticus,    09,    147 

Torcular   llerophili,    17 

Trabecuhe   subarailmoidealcs.   24 

Tract  of  Burdacli,   107 

Tract  of  fJoll,    107 

Tract   of    (Jower,    99 

Tract  of  Vicq  d'A/.yr,  79 


206 


ANATOMY  OP  THE  BRAIN 


Tractus   cerebio-tlialaiims,    175 

Tractus  olfactoiuus,   67,   129 

Tractus  opticus,  44,  131,  191 

Tractus     peduncvilaris     trans  versus,     84, 

159 
Tractus  pyrauiis  pedunculi  cerebri,  86 
Tractus  pyramidalis,  84 
Trapezium,  46,  90,  131 
Trifacial  nerve,  46 
Trigeminus,  46 
Trigonum  geniculatum,   104 
Trigonum  liabenulae,  53,  75,   133 
Trigonum  hypoglossi.   111 
Trigonum  lemnisci,   83,    104,   160 
Trigonum  vagi,    112 
Tuber  cinereum,  45,  51 
Tuberculum  acusticum,  91,  167 
Tuberculum   cuneatum,    107 
Tuberculum  gracile,   103 
Tuberculum  thalami  anterius,   70 
Tuberculum  thalami  posterius,   70,   147 
Turbinal  bones,  16 
Turner's  fissure,  41 
Vagus  nerve,  47 
Valve  of  Vieussens,  54 
Varoli,  pons,  45 
Vein  of  Galen.  20,  145 


Vi'lum  interpositum,   64 
Velum  medulhxre  anterium,  54 
Vena  cerebri  interna,  63 
Vena  cerebri  magna,  20,  53,  69,  145 
Vena  cerebri   posterior,   69 
Vena  cliorioidea,  63 
Vena  corporis  striati,   142 
Vena  frontalis,  21,  123 
Vena   jugularis   interna,    22 
Vena  oplithalmica,  22 
Vena  terminalis,  62,  145 
Vense   vertebrales,   22 
Ventral  pyramids,  97 
Ventricle  of  Arantius,    106 
Ventriculus  bulbi  olfactorii,  62,   169 
Ventriculi    laterales,    58,    61 
Ventriculus  medullse  spinalis,  54 
Ventriculus  quartus,  54,   110 
Ventriculus   tertius,   53,   80,    173 
Vermis  cerebelli,  38,   127 
Vermis   cerebelli   minor,   90,    177 
Vicq  d'Azyr,  tract  of,   79 
Vieussens,  valve  of,  54 
Willis,  circle  of,  30 
Willis,  portio,  dura  of,  90 
Willis,  portio,   mollis  of,   90 


i 


Date  Due 

misn 

149. 

'  ^01  'fc^ 

... 

, 



^ 

Nov  I 


t9l? 

COLUMBIA  UNIVERSITY  LIBRARIES  (hsi.stx)  " 

QM  34  691  C.2 

The  anatomy  of  the  brain: 


2002156725 


•V 


JUL  1 3 1949  ^uily '^^vuli 


HOV  ^  2  "^-  /1>4A 


